Update mocha requirement from ^2.0.1 to ^5.2.0

Updates the requirements on [mocha](https://github.com/mochajs/mocha) to permit the latest version.
- [Release notes](https://github.com/mochajs/mocha/releases)
- [Changelog](https://github.com/mochajs/mocha/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mochajs/mocha/commits/v5.2.0)

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

package.json

@@ -33,7 +33,7 @@
     "istanbul": "^0.4.0",
     "jscs": "^2.5.0",
     "jscs-preset-hexo": "^1.0.1",
-    "mocha": "^2.0.1"
+    "mocha": "^5.2.0"
   },
   "dependencies": {
     "hexo-pagination": "0.0.2"