fix(ng-package): add css/scss (#1044)

* fix(ng-package): add css/scss

Added assets configuration for CSS and SCSS files.

* Fix CSS file path formatting in ng-package.json

Author: Roman991

projects/ngx-toastr/ng-package.json

@@ -3,5 +3,9 @@
   "dest": "../../dist/ngx-toastr",
   "lib": {
     "entryFile": "src/public-api.ts"
-  }
+  },
+  "assets": [
+    "src/lib/*.css",
+    "src/lib/*.scss"
+  ]
 }