fix(package): update @angular-devkit/build-optimizer to version 0.6.1 (#2270)

Closes #2257

Author: mgechev

package.json

@@ -141,7 +141,7 @@
     "yargs": "^11.0.0"
   },
   "dependencies": {
-    "@angular-devkit/build-optimizer": "^0.5.0",
+    "@angular-devkit/build-optimizer": "^0.6.1",
     "@angular/animations": "^6.0.1",
     "@angular/common": "^6.0.1",
     "@angular/compiler": "^6.0.1",