support ruby < 2.3 and rails < 5.x

Author: syoder

.travis.yml

@@ -3,8 +3,10 @@ bundler_args: --binstubs --jobs=3 --retry=3
 cache: bundler
 sudo: false
 before_install:
-  - gem update --system
-  - gem install bundler
+  - gem i rubygems-update -v '<3' && update_rubygems
+  # from travis docs, to use bundler 1.x:
+  - gem uninstall -v '>= 2' -i $(rvm gemdir)@global -ax bundler || true
+  - gem install bundler -v '< 2'
 before_script:
   - "bin/ci-code-review"
 script: bin/ci