.travis.yml in avromatic-0.15.0 vs .travis.yml in avromatic-0.15.1

@@ -1,8 +1,12 @@
 language: ruby
 rvm:
-  - 2.2.4
-  - 2.3.1
+  - 2.4.0
+  - 2.3.3
+  - 2.2.6
+before_install:
+  # Workaround for https://github.com/sickill/rainbow/issues/48
+  - gem update --system
 before_script:
   - bundle exec appraisal install --jobs=3
 script:
   - bundle exec rubocop
   - bundle exec appraisal rails4_1 rake spec