Reduce supported ruby versions

Author: flori

.travis.yml

@@ -4,22 +4,14 @@ language: ruby
 
 # Specify which ruby versions you wish to run your tests on, each version will be used
 rvm:
-  - 1.8.7
-  - 1.9.2
-  - 1.9.3
   - 2.0.0
   - 2.1
   - 2.2
   - 2.3.3
   - 2.4.0
-  - ree
-  - ruby-head
 matrix:
   include:
     - rvm: jruby
       env: JRUBY_OPTS="--2.0"
-  allow_failures:
-    - rvm: rbx-2
-    - rvm: ruby-head
 script: "bundle exec rake"
 sudo: false