title: Cannot find module '@angular/core' when using PrimeNg
body: <p>I have installed PrimeNg and tried to use the sidebar component but when I run my project I get this error </p>
  
  <pre><code>ERROR in /home/haddad/projects/node_modules/primeng/components/sidebar/sidebar.d.ts (1,97): Cannot find module '@angular/core'.
  ERROR in Error: Metadata version mismatch for module /home/haddad/projects/node_modules/primeng/components/sidebar/sidebar.d.ts, found version 4, expected 3, resolving symbol AppModule in /home/haddad/projects/ar/arrt/src/app/app.module.ts, resolving symbol AppModule in /home/haddad/projects/ar/arrt/src/app/app.module.ts
  </code></pre>
  
  <p>I should use angular 4 , so I have modified PrimeNg version to 4.2.1 instead of 5v</p>
  
  <p>Here's <strong>package.json</strong> file </p>
  
  <pre><code>"dependencies": {
    "@angular/animations": "^4.3.4",
    "@angular/common": "~4.3.4",
    "@angular/compiler": "~4.3.4",
    "@angular/core": "~4.3.4",
    "@angular/forms": "~4.3.4",
    "@angular/http": "~4.3.4",
    "@angular/platform-browser": "~4.3.4",
    "@angular/platform-browser-dynamic": "~4.3.4",
    "@angular/router": "~4.3.4",
    "core-js": "^2.4.1",
    "primeng": "^4.2.1",
    "rxjs": "^5.5.6",
    "zone.js": "^0.8.19"
  },
  "devDependencies": {
    "@angular/cli": "1.6.6",
    "@angular/compiler-cli": "^4.3.4",
    "@angular/language-service": "^4.3.4",
    "@types/jasmine": "~2.8.3",
    "@types/jasminewd2": "~2.0.2",
    "@types/node": "~6.0.60",
    "codelyzer": "^4.0.1",
    "jasmine-core": "~2.8.0",
    "jasmine-spec-reporter": "~4.2.1",
    "karma": "~2.0.0",
    "karma-chrome-launcher": "~2.2.0",
    "karma-coverage-istanbul-reporter": "^1.2.1",
    "karma-jasmine": "~1.1.0",
    "karma-jasmine-html-reporter": "^0.2.2",
    "protractor": "~5.1.2",
    "ts-node": "~4.1.0",
    "tslint": "~5.9.1",
    "typescript": "~2.1.0"
  }
  </code></pre>
  
  <p>And my <strong>module.ts</strong> file :</p>
  
  <pre><code>import { BrowserModule } from '@angular/platform-browser';
  import { NgModule } from '@angular/core';
  import {SidebarModule} from 'primeng/sidebar';
  import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
  import { AppComponent } from './app.component';
  
  @NgModule({
    declarations: [
      AppComponent
    ],
    imports: [
      BrowserModule,SidebarModule,BrowserAnimationsModule
    ],
    providers: [],
    bootstrap: [AppComponent]
  })
  export class AppModule { }
  </code></pre>