require statements no longer work with latest minitest-rails gem

Within /lib/minitest/rails/shouldamatchers.rb there are a series of **require "minitest/rails/rails_libs"** statements that fail with:

    minitest-rails-shoulda/lib/minitest/rails/shoulda/matchers.rb:4:in `require': cannot load such file -- minitest/rails/active_support (LoadError)

Fixed by removing the 4 statements and doing a single require "minitest/rails" at the top of the matchers.rb.

***Note: Sorry I opened an issue first before realising I couldn't attach a pull request to it, which I assumed GitHub would allow.***

David