chore: replace angular-devkit/build-angular with ngtools/webpack

Author: SvetoslavTsenov

package.json

@@ -24,7 +24,7 @@
     "zone.js": "^0.8.26"
   },
   "devDependencies": {
-    "@angular-devkit/build-angular": "~0.7.0-rc.0",
+    "@ngtools/webpack": "6.1.0-rc.0",
     "@angular/compiler-cli": "~6.1.0-beta.3",
     "@types/chai": "~4.1.3",
     "@types/mocha": "~5.2.1",