chore(package): update nyc to version 15.1.0

Closes #114

Author: greenkeeper[bot]

package.json

@@ -72,7 +72,7 @@
     "mocha": "^6.0.2",
     "nock": "^10.0.6",
     "nodemon": "^1.18.10",
-    "nyc": "^14.0.0",
+    "nyc": "^15.1.0",
     "ts-node": "^8.0.2",
     "tslint": "^5.13.1",
     "typescript": "^3.3.3333"