fix(package): update yargs to version 12.0.1

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
  "semver": "^5.4.1",
  "update-notifier": "^2.3.0",
  "url-join": "^4.0.0",
- "yargs": "^11.0.0"
+ "yargs": "^12.0.1"
  },
  "devDependencies": {
  "ava": "^0.25.0",