fix(@angular/cli): add missing webpack-sources dep

`license-webpack-plugin` has a peer dependency on `webpack-sources` that was being satisfied via hoisting.

Fix #8075

Author: filipesilva

package.json

@@ -141,7 +141,8 @@
     "through": "^2.3.6",
     "ts-node": "^3.2.0",
     "tslint": "^5.1.0",
-    "walk-sync": "^0.3.1"
+    "walk-sync": "^0.3.1",
+    "webpack-sources": ">= 1.0.0"
   },
   "optionalDependencies": {
     "node-sass": "^4.3.0"

packages/@angular/cli/package.json

@@ -81,6 +81,7 @@
     "webpack-dev-middleware": "~1.12.0",
     "webpack-dev-server": "~2.7.1",
     "webpack-merge": "^4.1.0",
+    "webpack-sources": ">= 1.0.0",
     "webpack-subresource-integrity": "^1.0.1",
     "zone.js": "^0.8.14"
   },