Update shoulda-context requirement from ~> 1.2 to ~> 2.0

Updates the requirements on [shoulda-context](https://github.com/thoughtbot/shoulda-context) to permit the latest version.
- [Release notes](https://github.com/thoughtbot/shoulda-context/releases)
- [Changelog](https://github.com/thoughtbot/shoulda-context/blob/master/CHANGELOG.md)
- [Commits](thoughtbot/shoulda-context@v1.2.0...v2.0.0)

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

steam-condenser.gemspec

@@ -19,7 +19,7 @@ Gem::Specification.new do |s|
 
   s.add_development_dependency 'mocha', '~> 1.1'
   s.add_development_dependency 'rake', '~> 12.3'
-  s.add_development_dependency 'shoulda-context', '~> 1.2'
+  s.add_development_dependency 'shoulda-context', '~> 2.0'
   s.add_development_dependency 'test-unit', '~> 3.0'
   s.add_development_dependency 'yard', '~> 0.8'