.travis.yml in unibits-2.4.0 vs .travis.yml in unibits-2.5.0

@@ -3,11 +3,13 @@
 
 rvm:
 - ruby-head
 - 2.4.1
 - 2.4.0
+- 2.3.4
 - 2.3.3
-- 2.2
+- 2.2.7
+- 2.2.6
 - 2.1
 - 2.0
 - jruby-head
 - jruby-9.1.8.0