.travis.yml in heartcheck-1.5.0 vs .travis.yml in heartcheck-1.5.1

@@ -1,6 +1,6 @@
 language: ruby
-before_install: gem install bundler
+before_install: gem install bundler -v 1.17.3
 install: bundle install -j 4 --retry 3
 script:
   - bin/rspec
 matrix:
   include: