fix(@angular-devkit/build-webpack): support minor versions of webpack 4.x

Author: filipesilva

packages/angular_devkit/build_webpack/package.json

@@ -14,7 +14,7 @@
     "rxjs": "^6.0.0"
   },
   "peerDependencies": {
-    "webpack": "~4.6.0",
+    "webpack": "^4.6.0",
     "webpack-dev-server": "^3.1.4"
   }
 }