I think the problem was I had Angular 7 installed because after updating to 8 it works.

However I think I am still missing something because when I add this to my html (example from the documentation):

<a mdbBtn floating="true" size="lg" gradient="purple" mdbWavesEffect>
  <mdb-icon fas icon="bolt"></mdb-icon>
</a>
<a mdbBtn floating="true" gradient="peach" mdbWavesEffect>
  <mdb-icon fas icon="leaf"></mdb-icon>
</a>
<a mdbBtn floating="true" size="sm" gradient="blue" mdbWavesEffect>
  <mdb-icon fas icon="star"></mdb-icon>
</a>

Only the middle button (the one without a size attribute) is round. The other two are square.

Sorry for late reply.

Package.json file:

{
  "name": "mdbtest2",
  "version": "0.0.0",
  "scripts": {
    "ng": "ng",
    "start": "ng serve",
    "build": "ng build",
    "test": "ng test",
    "lint": "ng lint",
    "e2e": "ng e2e"
  },
  "private": true,
  "dependencies": {
    "@angular/animations": "~7.2.0",
    "@angular/common": "~7.2.0",
    "@angular/compiler": "~7.2.0",
    "@angular/core": "~7.2.0",
    "@angular/forms": "~7.2.0",
    "@angular/platform-browser": "~7.2.0",
    "@angular/platform-browser-dynamic": "~7.2.0",
    "@angular/router": "~7.2.0",
    "@fortawesome/fontawesome-free": "^5.12.0",
    "@types/chart.js": "^2.9.10",
    "animate.css": "^3.7.2",
    "chart.js": "^2.5.0",
    "core-js": "^2.5.4",
    "easy-pie-chart": "^2.1.7",
    "hammerjs": "^2.0.8",
    "ng-uikit-pro-standard": "git+https://oauth2:......@git.mdbootstrap.com/mdb/angular/ng-uikit-pro-standard.git",
    "rxjs": "~6.3.3",
    "screenfull": "^3.3.0",
    "tslib": "^1.9.0",
    "zone.js": "~0.8.26"
  },
  "devDependencies": {
    "@angular-devkit/build-angular": "~0.13.0",
    "@angular/cli": "~7.3.8",
    "@angular/compiler-cli": "~7.2.0",
    "@angular/language-service": "~7.2.0",
    "@types/node": "~8.9.4",
    "@types/jasmine": "~2.8.8",
    "@types/jasminewd2": "~2.0.3",
    "codelyzer": "~4.5.0",
    "jasmine-core": "~2.99.1",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~4.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "~2.0.1",
    "karma-jasmine": "~1.1.2",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.4.0",
    "ts-node": "~7.0.0",
    "tslint": "~5.11.0",
    "typescript": "~3.2.2"
  }
}

Angular.json file:

{
  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
  "version": 1,
  "newProjectRoot": "projects",
  "projects": {
    "mdbtest2": {
      "root": "",
      "sourceRoot": "src",
      "projectType": "application",
      "prefix": "app",
      "schematics": {
        "@schematics/angular:component": {
          "style": "scss"
        }
      },
      "architect": {
        "build": {
          "builder": "@angular-devkit/build-angular:browser",
          "options": {
            "outputPath": "dist/mdbtest2",
            "index": "src/index.html",
            "main": "src/main.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "src/tsconfig.app.json",
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ],
            "styles": [
              "node_modules/@fortawesome/fontawesome-free/scss/fontawesome.scss",
              "node_modules/@fortawesome/fontawesome-free/scss/solid.scss",
              "node_modules/@fortawesome/fontawesome-free/scss/regular.scss",
              "node_modules/@fortawesome/fontawesome-free/scss/brands.scss",
              "node_modules/ng-uikit-pro-standard/assets/scss/bootstrap/bootstrap.scss",
              "node_modules/ng-uikit-pro-standard/assets/scss/mdb.scss",
              "node_modules/animate.css/animate.css",
              "src/styles.scss"
            ],
            "scripts": [
              "node_modules/chart.js/dist/Chart.js",
              "node_modules/easy-pie-chart/dist/easypiechart.js",
              "node_modules/screenfull/dist/screenfull.js",
              "node_modules/hammerjs/hammer.min.js"
            ],
            "es5BrowserSupport": true
          },
          "configurations": {
            "production": {
              "fileReplacements": [
                {
                  "replace": "src/environments/environment.ts",
                  "with": "src/environments/environment.prod.ts"
                }
              ],
              "optimization": true,
              "outputHashing": "all",
              "sourceMap": false,
              "extractCss": true,
              "namedChunks": false,
              "aot": true,
              "extractLicenses": true,
              "vendorChunk": false,
              "buildOptimizer": true,
              "budgets": [
                {
                  "type": "initial",
                  "maximumWarning": "2mb",
                  "maximumError": "5mb"
                }
              ]
            }
          }
        },
        "serve": {
          "builder": "@angular-devkit/build-angular:dev-server",
          "options": {
            "browserTarget": "mdbtest2:build"
          },
          "configurations": {
            "production": {
              "browserTarget": "mdbtest2:build:production"
            }
          }
        },
        "extract-i18n": {
          "builder": "@angular-devkit/build-angular:extract-i18n",
          "options": {
            "browserTarget": "mdbtest2:build"
          }
        },
        "test": {
          "builder": "@angular-devkit/build-angular:karma",
          "options": {
            "main": "src/test.ts",
            "polyfills": "src/polyfills.ts",
            "tsConfig": "src/tsconfig.spec.json",
            "karmaConfig": "src/karma.conf.js",
            "styles": [
              "src/styles.scss"
            ],
            "scripts": [],
            "assets": [
              "src/favicon.ico",
              "src/assets"
            ]
          }
        },
        "lint": {
          "builder": "@angular-devkit/build-angular:tslint",
          "options": {
            "tsConfig": [
              "src/tsconfig.app.json",
              "src/tsconfig.spec.json"
            ],
            "exclude": [
              "**/node_modules/**"
            ]
          }
        }
      }
    },
    "mdbtest2-e2e": {
      "root": "e2e/",
      "projectType": "application",
      "prefix": "",
      "architect": {
        "e2e": {
          "builder": "@angular-devkit/build-angular:protractor",
          "options": {
            "protractorConfig": "e2e/protractor.conf.js",
            "devServerTarget": "mdbtest2:serve"
          },
          "configurations": {
            "production": {
              "devServerTarget": "mdbtest2:serve:production"
            }
          }
        },
        "lint": {
          "builder": "@angular-devkit/build-angular:tslint",
          "options": {
            "tsConfig": "e2e/tsconfig.e2e.json",
            "exclude": [
              "**/node_modules/**"
            ]
          }
        }
      }
    }
  },
  "defaultProject": "mdbtest2"
}