Merge pull request #22 from rollup-umd/greenkeeper/yargs-13.1.0

Update yargs to the latest version 🚀

Author: kopax

package.json

@@ -221,7 +221,7 @@
     "execa": "^1.0.0",
     "glob": "^7.1.3",
     "shelljs": "^0.8.3",
-    "yargs": "^12.0.5"
+    "yargs": "^13.1.0"
   },
   "peerDependencies": {},
   "publishConfig": {