chore(package): update nyc to version 15.0.0

Author: greenkeeper[bot]

package.json

@@ -36,7 +36,7 @@
     "karma-babel-preprocessor": "^8.0.0",
     "karma-jasmine": "^2.0.0",
     "karma-phantomjs-launcher": "^1.0.4",
-    "nyc": "^14.1.1",
+    "nyc": "^15.0.0",
     "p-event": "^4.1.0",
     "pify": "^4.0.0",
     "postcss": "^7.0.0",