Update travis testing to test on 2.x

Author: ioquatix

.travis.yml

@@ -1,7 +1,16 @@
+language: ruby
+sudo: false
+dist: trusty
+cache: bundler
 rvm:
-  - 1.9.3
-  - 2.0.0
-  - jruby
-branches:
-  only:
-    - master
+  - 2.0
+  - 2.1
+  - 2.2
+  - 2.3
+  - 2.4
+  - ruby-head
+  - jruby-head
+matrix:
+  allow_failures:
+    - rvm: "ruby-head"
+    - rvm: "jruby-head"