No provider for HttpClient

修改app.module.ts导入HttpClientModule.

...
import {HttpClientModule} from '@angular/common/http';

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    AppRoutingModule,
    HttpClientModule, // 导入此项
    FormsModule
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }