Bump mocha from 6.1.4 to 8.4.0

Bumps [mocha](https://github.com/mochajs/mocha) from 6.1.4 to 8.4.0.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](mochajs/mocha@v6.1.4...v8.4.0)

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

package.json

@@ -18,7 +18,7 @@
     "coveralls": "3.0.4",
     "koa": "2.7.0",
     "koa-mount": "4.0.0",
-    "mocha": "6.1.4",
+    "mocha": "8.4.0",
     "mocha-lcov-reporter": "1.3.0",
     "nyc": "14.1.1",
     "supertest": "4.0.2"