chore(package): update nyc to version 15.1.0

Closes #138

Author: greenkeeper[bot]

package.json

@@ -45,7 +45,7 @@
     "coveralls": "^3.0.0",
     "github-release-from-changelog": "^2.0.0",
     "npm-run-all": "^4.1.1",
-    "nyc": "^13.2.0",
+    "nyc": "^15.1.0",
     "rimraf": "^3.0.0",
     "tslint": "^5.8.0",
     "typescript": "3.3"