Update mocha requirement from ~> 1.0 to ~> 2.7

Updates the requirements on [mocha](https://github.com/freerange/mocha) to permit the latest version.
- [Changelog](https://github.com/freerange/mocha/blob/main/RELEASE.md)
- [Commits](freerange/mocha@v1.0.0...v2.7.1)

---
updated-dependencies:
- dependency-name: mocha
  dependency-version: 2.7.1
  dependency-type: direct:development
...

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

Author: dependabot[bot]

Gemfile

@@ -22,7 +22,7 @@ group :development do
 
   gem 'mdl', '~> 0.11.0'
 
-  gem 'mocha', '~> 1.0'
+  gem 'mocha', '~> 2.7'
 
   gem 'rake'
   gem 'rspec', '~> 3.1'