Merge pull request rails-api#2310 from krzysiek1507/fix/bundler-on-travis

Install bundler ~> 1.17 on Travis

Author: bf4

.travis.yml

@@ -6,9 +6,9 @@ cache:
     - vendor/bundle
 
 before_install:
-  - "travis_retry gem update --system"
-  - "travis_retry gem update bundler"
-install: bundle install --path=vendor/bundle --retry=3 --jobs=3
+  - "travis_retry gem update --system 2.7.8"
+  - "travis_retry gem install bundler -v '1.17.3'"
+install: BUNDLER_VERSION=1.17.3 bundle install --path=vendor/bundle --retry=3 --jobs=3
 
 script:
   - bundle exec rake ci
@@ -48,6 +48,7 @@ matrix:
   - { rvm: 2.1.10,        env: RAILS_VERSION=master }
   - { rvm: 2.2.8,        env: RAILS_VERSION=master }
   - { rvm: 2.3.5,        env: RAILS_VERSION=master }
+  - { rvm: 2.4.2,        env: RAILS_VERSION=master }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.0 }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.1 }
   - { rvm: 2.1.10,        env: RAILS_VERSION=5.2 }