Bump mocha from 2.5.0 to 2.6.0

Bumps [mocha](https://github.com/freerange/mocha) from 2.5.0 to 2.6.0.
- [Changelog](https://github.com/freerange/mocha/blob/main/RELEASE.md)
- [Commits](freerange/mocha@v2.5.0...v2.6.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile.lock

@@ -248,7 +248,7 @@ GEM
     method_source (1.1.0)
     mini_mime (1.1.5)
     minitest (5.25.1)
-    mocha (2.5.0)
+    mocha (2.6.0)
       ruby2_keywords (>= 0.0.5)
     msgpack (1.7.2)
     multi_xml (0.7.1)