.travis.yml in rakuten_web_service-1.9.1 vs .travis.yml in rakuten_web_service-1.9.2

@@ -1,9 +1,10 @@
 language: ruby
 rvm:
   - 2.3.6
   - 2.4.3
   - 2.5.0
+  - 2.6.0
   - ruby-head
 
 env:
   - INTEGRATION=yes
   - INTEGRATION=no