thoughtbot/paperclip — pull request #1463 by takashi (2014-02-26 12:17:27+00:00)
Title: Update rspec matcher protocol for rspec3.0

When I run rspec with `Paperclip::Shoulda::Matchers`,

I could see the error like below.
```
Paperclip::Shoulda::Matchers::HaveAttachedFileMatcher implements a legacy RSpec matcher
protocol. For the current protocol you should expose the failure messages
via the `failure_message` and `failure_message_when_negated` methods.
```

In RSpec3.0, failure messages methods in matchers are updated to ` failure_message` and `failure_message_negated`

So I changed methods in matchers.