chore(package): update yargs to version 7.0.2

https://greenkeeper.io/

Author: greenkeeperio-bot

package.json

@@ -40,7 +40,7 @@
     "globby": "^6.1.0",
     "post-load-plugins": "0.0.13",
     "posthtml": "^0.9.2",
-    "yargs": "^6.6.0"
+    "yargs": "^7.0.2"
   },
   "devDependencies": {
     "path-exists": "^3.0.0",