.travis.yml in fluent-plugin-rename-key-0.1.3 vs .travis.yml in fluent-plugin-rename-key-0.1.4

@@ -1,7 +1,10 @@
 language: ruby
 
 rvm:
-  - 2.0.0
+  - 2.3.0
+  - 2.2
   - 1.9.3
-  - rbx-19mode
 
+# to avoid travis-ci issue since 2015-12-25
+before_install:
+  - gem update bundler