chore(package): update yargs to version 15.3.0

Closes #37

Author: greenkeeper[bot]

demo/package.json

@@ -74,7 +74,7 @@
     "typescript": "~3.2.4",
     "webpack-cli": "^3.2.3",
     "webpack-node-externals": "~1.7.2",
-    "yargs": "^12.0.5"
+    "yargs": "^15.3.0"
   },
   "jest": {
     "preset": "jest-preset-angular",