bumps travis elixir 1.7.x release

Author: mneudert

.travis.yml

@@ -17,12 +17,12 @@ jobs:
       elixir: 1.6.6
       otp_release: 21.0
     - <<: *test
-      elixir: 1.7.3
+      elixir: 1.7.4
       otp_release: 21.0
       after_success: mix coveralls.travis
 
     - stage: code quality
-      elixir: 1.7.3
+      elixir: 1.7.4
       otp_release: 21.0
       script:
         - mix format --check-formatted