.travis.yml in relaton-iso-bib-0.2.3 vs .travis.yml in relaton-iso-bib-0.2.4

@@ -4,14 +4,15 @@
 cache: bundler
 os:
 - linux
 - osx
 rvm:
+- 2.6
 - 2.5
 - 2.4
 - ruby-head
-before_install:
-- gem install bundler -v 2.0.1
+before_install: 
+- gem install bundler -v "~> 2"
 - bundle update
 matrix:
   allow_failures:
     - rvm: ruby-head