Bump mocha from 6.2.3 to 9.0.0

Bumps [mocha](https://github.com/mochajs/mocha) from 6.2.3 to 9.0.0.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](mochajs/mocha@v6.2.3...v9.0.0)

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

package.json

@@ -23,7 +23,7 @@
     "eslint-config-hexo": "^4.0.0",
     "hexo": "^4.0.0",
     "hexo-unique-post-path": "file:.",
-    "mocha": "^6.2.1",
+    "mocha": "^9.0.0",
     "moment": "^2.24.0",
     "nyc": "^14.1.1",
     "sinon": "^7.5.0"