title: error TS5023: Unknown compiler option 'enableIvy'
body: <p>I am trying to add IVY to my angular 7 beta project. So, I added <code>enableIvy: true</code> to <code>src/tsconfig.app.json</code> in <code>compilerOptions</code> section</p>
  
  <p>But when I run <code>ng build --prod --aot --output-hashing none</code> I get below error.</p>
  
  <pre><code>error TS5023: Unknown compiler option 'enableIvy'.
  
  Error: error TS5023: Unknown compiler option 'enableIvy'.
  
      at AngularCompilerPlugin._setupOptions (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@ngtools/webpack/src/angular_compiler_plugin.js:112:19)
      at new AngularCompilerPlugin (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@ngtools/webpack/src/angular_compiler_plugin.js:61:14)
      at _createAotPlugin (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/src/angular-cli-files/models/webpack-configs/typescript.js:41:12)
      at Object.getAotConfig (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/src/angular-cli-files/models/webpack-configs/typescript.js:63:19)
      at BrowserBuilder.buildWebpackConfig (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/src/browser/index.js:81:37)
      at MergeMapSubscriber.rxjs_1.of.pipe.operators_1.concatMap [as project] (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/src/browser/index.js:31:38)
      at MergeMapSubscriber._tryNext (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/operators/mergeMap.js:65:27)
      at MergeMapSubscriber._next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/operators/mergeMap.js:55:18)
      at MergeMapSubscriber.Subscriber.next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/Subscriber.js:64:18)
      at TapSubscriber._next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/operators/tap.js:62:26)
      at TapSubscriber.Subscriber.next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/Subscriber.js:64:18)
      at MergeMapSubscriber.notifyNext (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/operators/mergeMap.js:84:26)
      at InnerSubscriber._next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/InnerSubscriber.js:25:21)
      at InnerSubscriber.Subscriber.next (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/Subscriber.js:64:18)
      at ForkJoinSubscriber.notifyComplete (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/observable/forkJoin.js:79:25)
      at InnerSubscriber._complete (/Users/k26686/aniruddh/develop/experiment/shepherd/node_modules/@angular-devkit/build-angular/node_modules/rxjs/internal/InnerSubscriber.js:32:21)
  </code></pre>
  
  <p>Any one resolved this.</p>