.travis.yml in relaton-ietf-0.5.3 vs .travis.yml in relaton-ietf-0.5.4

@@ -8,10 +8,10 @@
 rvm:
 - 2.5
 - 2.4
 - ruby-head
 before_install: 
-- gem install bundler -v 2.0.1
+- gem install bundler -v "~> 2"
 - bundle update
 matrix:
   allow_failures:
     - rvm: ruby-head