.travis.yml in metanorma-gb-1.0.12 vs .travis.yml in metanorma-gb-1.1.0

@@ -5,10 +5,10 @@
   - 2.5
   - 2.4
   - 2.3
   - ruby-head
 before_install:
-  - gem install bundler -v 1.16.1
+  - gem install bundler -v 2.0.1
   - unset _JAVA_OPTIONS
 matrix:
   allow_failures:
     - rvm: ruby-head