chore(package): update nyc to version 15.1.0

Closes #118

Author: greenkeeper[bot]

Diff for: package.json

@@ -108,7 +108,7 @@
     "generate-release": "^0.14.0",
     "nodemon": "^1.12.1",
     "nsp": "^3.0.0",
-    "nyc": "^11.2.1",
+    "nyc": "^15.1.0",
     "uuid": "^3.1.0"
   }
 }