fix(package): update yargs to version 14.0.0

Author: greenkeeper[bot]

package.json

@@ -39,7 +39,7 @@
     "source-map-url": "^0.4.0",
     "unixify": "^1.0.0",
     "yargonaut": "^1.1.2",
-    "yargs": "^13.1.0"
+    "yargs": "^14.0.0"
   },
   "devDependencies": {
     "ava": "^1.0.1",