chore(package): update nyc to version 15.0.1

Closes #8

Author: greenkeeper[bot]

package.json

@@ -43,7 +43,7 @@
     "chai": "^4.2.0",
     "husky": "^3.0.0",
     "mocha": "^6.0.2",
-    "nyc": "^14.0.0",
+    "nyc": "^15.0.1",
     "semistandard": "^14.0.1"
   }
 }