Merge pull request #712 from aycabta/use-2.4.6

Use Ruby 2.4.6 for test

Author: aycabta

.travis.yml

@@ -5,7 +5,7 @@ before_install:
 language: ruby
 rvm:
   - 2.3.8
-  - 2.4.5
+  - 2.4.6
   - 2.5.5
   - 2.6.2
   - ruby-head