.travis.yml in metanorma-gb-1.2.2 vs .travis.yml in metanorma-gb-1.2.3

@@ -4,9 +4,10 @@
 cache: bundler
 os:
 - linux
 - osx
 rvm:
+- 2.6
 - 2.5
 - 2.4
 - ruby-head
 before_install: 
 - gem install bundler -v "~> 2"