Bump mocha from 2.3.0 to 2.4.0 (#878)

Bumps [mocha](https://github.com/freerange/mocha) from 2.3.0 to 2.4.0.
- [Changelog](https://github.com/freerange/mocha/blob/main/RELEASE.md)
- [Commits](https://github.com/freerange/mocha/compare/v2.3.0...v2.4.0)

---
updated-dependencies:
- dependency-name: mocha
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Gemfile.lock

@@ -254,7 +254,7 @@ GEM
     mini_magick (4.12.0)
     mini_mime (1.1.5)
     minitest (5.23.1)
-    mocha (2.3.0)
+    mocha (2.4.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
     net-http (0.4.1)