chore(package): update nyc to version 15.0.0

Closes #8

Author: greenkeeper[bot]

package.json

@@ -33,7 +33,7 @@
     "mocha": "5.2.0",
     "mocha-typescript": "1.1.17",
     "mochawesome": "3.1.1",
-    "nyc": "13.2.0",
+    "nyc": "15.0.0",
     "prettier": "1.16.4",
     "rimraf": "2.6.3",
     "source-map-support": "0.5.10",