chore(package): update nyc to version 15.1.0

Closes #33

Author: greenkeeper[bot]

package.json

@@ -58,7 +58,7 @@
     "eslint-plugin-ava": "7.1.0",
     "eslint-plugin-prettier": "3.1.0",
     "nodemon": "1.19.1",
-    "nyc": "14.1.1",
+    "nyc": "15.1.0",
     "prettier": "1.18.2",
     "sinon": "7.4.1",
     "source-map-support": "0.5.13",