chore(package): update yargs to version 15.3.0

Closes #37

Author: greenkeeper[bot]

package.json

@@ -105,7 +105,7 @@
     "tslint": "^5.14.0",
     "typescript": "~3.1.6",
     "webpack-node-externals": "^1.7.2",
-    "yargs": "^12.0.5",
+    "yargs": "^15.3.0",
     "zone.js": "^0.8.26"
   },
   "engines": {