Bump nyc from 11.9.0 to 15.0.1

Bumps [nyc](https://github.com/istanbuljs/nyc) from 11.9.0 to 15.0.1.
- [Release notes](https://github.com/istanbuljs/nyc/releases)
- [Changelog](https://github.com/istanbuljs/nyc/blob/master/CHANGELOG.md)
- [Commits](istanbuljs/nyc@v11.9.0...v15.0.1)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

package.json

@@ -19,7 +19,7 @@
     "eslint-plugin-standard": "^3.1.0",
     "mocha": "^6.1.4",
     "mocha-lcov-reporter": "^1.3.0",
-    "nyc": "^11.9.0"
+    "nyc": "^15.0.1"
   },
   "peerDependencies": {
     "ajv": ">=4.11.8"