Update mocha requirement from ^3.2.0 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

@@ -39,6 +39,6 @@
     "istanbul": "^0.4.5",
     "jscs": "^3.0.7",
     "jscs-preset-hexo": "^1.0.1",
-    "mocha": "^3.2.0"
+    "mocha": "^5.2.0"
   }
 }