chore(package): update nyc to version 15.0.1

Closes #20

Author: greenkeeper[bot]

Diff for: package.json

@@ -46,7 +46,7 @@
     "ava": "0.25.0",
     "coveralls": "3.0.9",
     "minami": "^1.2.3",
-    "nyc": "14.1.1",
+    "nyc": "15.0.1",
     "standard": "14.3.1"
   },
   "nyc": {