.travis.yml in ahoy_email-0.5.0 vs .travis.yml in ahoy_email-0.5.1

@@ -1,15 +1,16 @@
 language: ruby
 rvm:
-  - 2.3.0
+  - 2.4.2
 sudo: false
 script: bundle exec rake test
 before_script:
   - gem install bundler
 notifications:
   email:
     on_success: never
     on_failure: change
 gemfile:
   - Gemfile
+  - test/gemfiles/actionmailer51.gemfile
   - test/gemfiles/actionmailer50.gemfile
   - test/gemfiles/actionmailer42.gemfile