chore(package): update yargs to version 9.0.1

Closes #61

Author: greenkeeper[bot]

package.json

@@ -47,7 +47,7 @@
     "mocha-junit-reporter": "^1.13.0",
     "run-sequence": "^1.2.2",
     "standard": "^9.0.2",
-    "yargs": "^7.0.2"
+    "yargs": "^9.0.1"
   },
   "greenkeeper": {
     "ignore": [