Bump mocha from 1.1.0 to 1.8.0

Bumps [mocha](https://github.com/freerange/mocha) from 1.1.0 to 1.8.0.
- [Release notes](https://github.com/freerange/mocha/releases)
- [Changelog](https://github.com/freerange/mocha/blob/master/RELEASE.md)
- [Commits](freerange/mocha@v1.1.0...v1.8.0)

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

Gemfile.lock

@@ -43,7 +43,7 @@ GEM
     metaclass (0.0.4)
     mime-types (2.6.2)
     minitest (4.7.5)
-    mocha (1.1.0)
+    mocha (1.8.0)
       metaclass (~> 0.0.1)
     multi_json (1.12.1)
     rack (1.5.5)