use ruby 2.6.1

Colby Swandale · Colby Swandale · commit 204390714916 · 2019-02-05T00:19:11.000+11:00
diff --git a/.travis.yml b/.travis.yml
@@ -4,7 +4,7 @@ rvm:
   - 2.3.8
   - 2.4.5
   - 2.5.3
-  - 2.6.0
+  - 2.6.1
   - ruby-head
 script: rake test
 matrix:
