Upgrade yargs to v6

Author: SpaceK33z

package.json

@@ -20,7 +20,7 @@
     "strip-ansi": "^3.0.0",
     "supports-color": "^3.1.1",
     "webpack-dev-middleware": "^1.4.0",
-    "yargs": "^4.7.1"
+    "yargs": "^6.0.0"
   },
   "devDependencies": {
     "css-loader": "~0.25.0",