chore(package): update nyc to version 15.0.0

Closes #297

Author: greenkeeper[bot]

package.json

@@ -55,7 +55,7 @@
     "jsdom": "11.1.0",
     "mocha": "3.4.2",
     "npm-run-all": "4.0.2",
-    "nyc": "^11.1.0",
+    "nyc": "^15.0.0",
     "react": "^16.3.0",
     "react-dom": "^16.3.0",
     "react-router": "^3.0.4",