Bump nyc from 14.1.1 to 15.0.1

Bumps [nyc](https://github.com/istanbuljs/nyc) from 14.1.1 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@v14.1.1...v15.0.1)

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

package.json

@@ -20,7 +20,7 @@
     "koa-mount": "4.0.0",
     "mocha": "6.1.4",
     "mocha-lcov-reporter": "1.3.0",
-    "nyc": "14.1.1",
+    "nyc": "15.0.1",
     "supertest": "4.0.2"
   },
   "license": "MIT",