Switch to rspec 3.0 failure message declarations
Specify which matcher syntax to use

Since we're using `should` syntax, we need to explicitly enable it to
avoid deprecation warnings in rspec 3.0.
Provide ci builds for rspec 3.0
Enable builds for RSpec 3.0
Merge pull request #7 from westarete/support-for-rspec-3.0

Support for RSpec 3.0