chore(package): update joi to version 8.4.2

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -94,7 +94,7 @@
     "webpack-merge": "0.12.0"
   },
   "dependencies": {
-    "joi": "8.0.5",
+    "joi": "8.4.2",
     "joi-browser": "8.0.5",
     "vue": "1.0.21"
   },