fix(package): update yargs to version 15.0.2

Closes #22

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "mkdirp": "^0.5.1",
     "react": "^15.4.1",
     "react-docgen": "^2.13.0",
-    "yargs": "^8.0.1"
+    "yargs": "^15.0.2"
   },
   "devDependencies": {
     "babel-eslint": "^7.1.1",