Update the list of rubies

Obsolete versions are removed since they always fail in bundle.

Author: knu

.travis.yml

@@ -4,15 +4,11 @@ env:
     - JRUBY_OPTS="$JRUBY_OPTS --debug"
 language: ruby
 rvm:
-  - 1.8.7
-  - 1.9.3
-  - 2.0.0
   - 2.1
   - 2.2
-  - jruby-18mode
-  - jruby-19mode
+  - 2.3.1
+  - jruby-9
   - jruby-head
-  - rbx-2
   - ruby-head
 matrix:
   allow_failures: