Loosen aspnet-webpack peerDependency requirement back to cover what it allowed before (so it's not a breaking change)

src/Microsoft.AspNetCore.SpaServices/npm/aspnet-webpack/package.json

@@ -33,6 +33,6 @@
     "webpack": "^1.13.2"
   },
   "peerDependencies": {
-    "webpack": "^1.13.2 || ^2.2.0 || ^3.0.0"
+    "webpack": "^1.13.2 || ^2.1.0-beta || ^3.0.0"
   }
 }