chore(package): update nyc to version 15.1.0

Closes #32

Author: greenkeeper[bot]

package.json

@@ -53,7 +53,7 @@
     "mocha": "6.2.0",
     "nock": "10.0.6",
     "node-typescript": "0.1.3",
-    "nyc": "14.1.1",
+    "nyc": "15.1.0",
     "prettier": "1.18.2",
     "rewire": "4.0.1",
     "source-map-support": "0.5.12",