Bump nyc from 14.1.1 to 15.0.0

Bumps [nyc](https://github.com/istanbuljs/nyc) from 14.1.1 to 15.0.0.
- [Release notes](https://github.com/istanbuljs/nyc/releases)
- [Changelog](https://github.com/istanbuljs/nyc/blob/master/CHANGELOG.md)
- [Commits](istanbuljs/nyc@v14.1.1...v15.0.0)

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

package.json

@@ -59,7 +59,7 @@
     "chai": "^4.2.0",
     "coveralls": "^3.0.3",
     "mocha": "^6.0.2",
-    "nyc": "^14.1.1",
+    "nyc": "^15.0.0",
     "source-map-support": "^0.5.10",
     "ts-node": "^8.0.2",
     "typescript": "^3.3.3333"