Make CI run on Ruby 2.6

dlackty · dlackty · commit f454dc5a0583 · 2019-01-19T21:22:03.000+08:00
diff --git a/.travis.yml b/.travis.yml
@@ -4,6 +4,7 @@ rvm:
   - 2.3
   - 2.4
   - 2.5
+  - 2.6
   - ruby-head
 before_install:
   - if [ ${TRAVIS_RUBY_VERSION} = '2.2' ]; then
