chore(package): update nyc to version 15.0.1

Closes #92

Author: greenkeeper[bot]

package.json

@@ -57,7 +57,7 @@
     "lokka-transport-http": "1.6.1",
     "mocha": "5.2.0",
     "mocha-performance": "0.1.1",
-    "nyc": "11.8.0",
+    "nyc": "15.0.1",
     "swagger-tools": "0.10.4",
     "typedoc": "^0.12.0",
     "typedoc-plugin-external-module-name": "^1.1.1",