chore(package): update nyc to version 15.0.0

Closes #22

Author: greenkeeper[bot]

package.json

@@ -32,7 +32,7 @@
     "inspect-process": "^0.5.0",
     "istanbul": "^0.4.5",
     "mocha": "^6.0.0",
-    "nyc": "^13.2.0",
+    "nyc": "^15.0.0",
     "standard": "^12.0.0"
   },
   "standard": {