Take dependency on newer webpack-dev-middleware because it fixes ambiguities in path handling

Author: SteveSandersonMS

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

@@ -21,7 +21,7 @@
     "es6-promise": "^3.1.2",
     "memory-fs": "^0.3.0",
     "require-from-string": "^1.1.0",
-    "webpack-dev-middleware": "^1.6.1",
+    "webpack-dev-middleware": "^1.8.4",
     "webpack-node-externals": "^1.4.3"
   },
   "devDependencies": {