fix imports

Author: LexDX

angular/src/app/app.module.ts

@@ -2,7 +2,7 @@ import { BrowserModule } from '@angular/platform-browser';
 import { NgModule } from '@angular/core';
 import { AppComponent } from './app.component';
 
-import { DxDropDownButtonModule } from 'devextreme-angular';
+import { DxDropDownButtonModule } from 'devextreme-angular/ui/drop-down-button';
 
 @NgModule({
     declarations: [
@@ -15,4 +15,4 @@ import { DxDropDownButtonModule } from 'devextreme-angular';
     providers: [ ],
     bootstrap: [AppComponent]
 })
-export class AppModule { }
+export class AppModule { }