chore: add build script

Author: bobbyg603

package.json

@@ -6,6 +6,7 @@
     "start": "ng serve",
     "build": "ng build",
     "build:prod": "ng build --configuration production",
+    "build:example": "ng build ngx-animated-counter-example --configuration production --base-href /ngx-animated-counter-example/",
     "test": "ng test",
     "lint": "ng lint",
     "release": "npm run build:prod && cd dist/@bugsplat/ngx-animated-counter && npm publish -access public"