title: Cannot find module 'rxjs-compat/Observable'
body: <p>I am currently upgrading angular 4 to angular 6 code. I have installed "rxjs": "^6.3.2" and un-installed rxjs-compact as I have migrated the code to use the new rxjs operators. I am still getting the following errors. Dont know the reason why</p>
  
  <pre><code>ERROR in [at-loader] ./node_modules/rxjs/BehaviorSubject.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/BehaviorSubject'.
  
  ERROR in [at-loader] ./node_modules/rxjs/Observable.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/Observable'.
  
  ERROR in [at-loader] ./node_modules/rxjs/Observer.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/Observer'.
  
  ERROR in [at-loader] ./node_modules/rxjs/Operator.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/Operator'.
  
  ERROR in [at-loader] ./node_modules/rxjs/Subject.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/Subject'.
  
  ERROR in [at-loader] ./node_modules/rxjs/Subscription.d.ts:1:15
      TS2307: Cannot find module 'rxjs-compat/Subscription'.
  </code></pre>