Don't test REE [ci skip]

Ruby Enterprise Edition has reached its end of life and should be fully
compatible with MRI 1.8.7. Testing on both is wasting resources. See:
http://blog.phusion.nl/2012/02/21/ruby-enterprise-edition-1-8-7-2012-02-released-end-of-life-imminent/

.travis.yml

@@ -1,13 +1,12 @@
+script: "bundle exec rake spec cucumber"
+
 rvm:
   - 1.8.7
   - 1.9.2
   - 1.9.3
-  - ree
   - rbx-18mode
   - jruby
 
-script: "bundle exec rake spec cucumber"
-
 gemfile:
   - gemfiles/3.0.gemfile
   - gemfiles/3.1.gemfile
@@ -17,3 +16,12 @@ matrix:
   allow_failures:
     - rvm: rbx-18mode
     - rvm: jruby
+  exclude:
+    - rvm: rbx-18mode
+      gemfile: gemfiles/3.0.gemfile
+    - rvm: rbx-18mode
+      gemfile: gemfiles/3.1.gemfile
+    - rvm: jruby
+      gemfile: gemfiles/3.0.gemfile
+    - rvm: jruby
+      gemfile: gemfiles/3.1.gemfile