Update ruby versions

Author: laurynas

.travis.yml

@@ -1,13 +1,12 @@
 rvm:
-- 1.9.3
-- 2.0.0
-- 2.1.1
-- 2.3.4
-- 2.4.1
-- 2.5.0
+- 2.0
+- 2.1
+- 2.3
+- 2.4
+- 2.5
+- 2.6
 - ruby-head
 - ruby-head-clang
-- jruby-1.7
 - jruby-9.1
 - jruby-head
 script: bundle exec rake spec