Do no use should for spec names (#36)

- Remove the word should from the spec names
- Add a gem that will prevent to this happen again
Use the the method `expect` instead of `should` (#36)

- Replace all the should statements for expect
- Configure RSpec to use only expect assertions
Merge branch 'master' of github.com:thoughtworks/pacto into remove_should_from_specs

Conflicts:
	spec/spec_helper.rb
	spec/unit/pacto/core/contract_repository_spec.rb
betterspecs - method labeling convention
betterspecs - method labeling convention [ci_skip]
Merge pull request #37 from thoughtworks/remove_should_from_specs

Merging remove should from specs

Reviewed and think I fixed all the method descriptions.  I'm going to go ahead and merge.  If you find any others we'll fix them.