Merge pull request #278 from aycabta/use-ruby-2.5.3

Use Ruby 2.2.10, 2.3.8, 2.4.5, and 2.5.3

Author: hsbt

.travis.yml

@@ -3,10 +3,10 @@ sudo: false
 rvm:
   - 2.0.0
   - 2.1.10
-  - 2.2.9
-  - 2.3.6
-  - 2.4.3
-  - 2.5.0
+  - 2.2.10
+  - 2.3.8
+  - 2.4.5
+  - 2.5.3
   - ruby-head
   - jruby-9.1.16.0
   - jruby-head