Merge pull request #39 from olleolleolle/patch-1

Travis: Update CI matrix

Author: javierjulio

.travis.yml

@@ -3,14 +3,13 @@ language: ruby
 before_install:
   - gem update --system
   - gem install bundler
-  - gem update bundler
 
 rvm:
-  - 2.1.9
-  - 2.2.6
-  - 2.3.3
-  - 2.4.0
-  - jruby-9.0.5.0
+  - 2.1.10
+  - 2.2.7
+  - 2.3.4
+  - 2.4.1
+  - jruby-9.1.10.0
   - jruby-head
 
 cache: bundler