fix(package): update yargs to version 15.0.2

Closes #13

Author: greenkeeper[bot]

package.json

@@ -42,6 +42,6 @@
     "clui": "^0.3.6",
     "colors": "^1.1.2",
     "metakit": "^0.2.0",
-    "yargs": "^11.0.0"
+    "yargs": "^15.0.2"
   }
 }