chore(package): update nyc to version 15.0.1

Closes #126

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
     "babel-cli": "^6.26.0",
     "chai": "^4.2.0",
     "mocha": "^6.1.4",
-    "nyc": "^14.1.1",
+    "nyc": "^15.0.1",
     "rimraf": "^2.6.3",
     "supertest": "3.4.0",
     "tslint": "^5.11.0",