.travis.yml in asciidoctor-htmlbook-0.0.4 vs .travis.yml in asciidoctor-htmlbook-0.0.5

@@ -2,6 +2,6 @@
 language: ruby
 rvm:
   - 2.4
   - 2.5
   - 2.6
-before_install: gem install bundler -v 1.13.7
+before_install: gem install bundler -v 2.0.2