Fix bootstrapping

Author: Heatmanofurioso

projects/lib/src/directives/google-signin-button.module.ts

@@ -2,7 +2,10 @@ import { NgModule } from '@angular/core';
 import { GoogleSigninButtonDirective } from './google-signin-button.directive';
 
 @NgModule({
-  declarations: [GoogleSigninButtonDirective],
+  declarations: [],
   exports: [GoogleSigninButtonDirective],
+  imports: [
+    GoogleSigninButtonDirective
+  ]
 })
 export class GoogleSigninButtonModule {}