fix(package): update yargs to version 15.3.0

Closes #485

Author: greenkeeper[bot]

package.json

@@ -28,7 +28,7 @@
     "sanitize-html": "^1.13.0",
     "socket.io-client": "^2.0.0",
     "string": "^3.3.1",
-    "yargs": "^12.0.1"
+    "yargs": "^15.3.0"
   },
   "devDependencies": {
     "bithound": "^1.7.0",