feat(@angular-devkit/build-angular): update webpack to 4.29

This version (https://github.com/webpack/webpack/releases/tag/v4.29.0) includes a memory leak fix for assets (webpack/webpack#8609, webpack/webpack#8642).

Thanks to @Meligy for pinging about this!

package.json

@@ -36,6 +36,6 @@
     "@angular/compiler": "^7.2.0-rc.0",
     "@angular/compiler-cli": "^7.2.0-rc.0",
     "typescript": "3.2.4",
-    "webpack": "4.28.4"
+    "webpack": "4.29.0"
   }
 }