Upgrade node-sass to 4.9.0

[Fixes #513] Angular template incompatible with NodeJs 10

src/Microsoft.DotNet.Web.Spa.ProjectTemplates/content/Angular-CSharp/ClientApp/package.json

@@ -49,5 +49,8 @@
     "ts-node": "~4.1.0",
     "tslint": "~5.9.1",
     "typescript": "~2.5.3"
+  },
+  "optionalDependencies": {
+    "node-sass": "^4.9.0"
   }
 }