.travis.yml in rack-simple_user_agent-0.3.0 vs .travis.yml in rack-simple_user_agent-0.4.0

@@ -1,6 +1,8 @@
 language: ruby
 cache: bundler
 rvm:
   - 2.2.5
-  - 2.3.1
-before_install: gem install bundler -v 1.11.2
+  - 2.3.7
+  - 2.4.5
+  - 2.5.3
+before_install: gem update bundler