.travis.yml in asciidoctor-htmlbook-0.0.5 vs .travis.yml in asciidoctor-htmlbook-0.0.6

@@ -2,6 +2,7 @@
 language: ruby
 rvm:
   - 2.4
   - 2.5
   - 2.6
-before_install: gem install bundler -v 2.0.2
+  - 2.7
+before_install: gem install bundler -v 2.1.4