Use be false/be true instead of be_true/be_false. Silences deprecations.
Upgrade to rspec 3. Add rspec-its and rspec-collection_matchers gem
Infer spec type from location
remove rspec deprecations
Upgrade to rspec 3.1
Merge pull request #326 from mailboxer/rspec_3

Rspec 3
Refactor receipts to avoid SQLite3::RangeException in Rails 4.2
Inspired by
https://github.com/seankay/mailboxer/commit/f1096e2593708ff44c17e0bee1b9fb9566b31b49
Thanks @seankay!
New testing matrix