TravisCI: allow puppet 2.7 to fail

.travis.yml

@@ -9,10 +9,7 @@ rvm:
 matrix:
   allow_failures:
     - rvm: 1.8.7
-    - rvm: 2.0.0
-      env: PUPPET_VERSION="2.7"
-    - rvm: 2.1.5
-      env: PUPPET_VERSION="2.7"
+    - env: PUPPET_VERSION="2.7"
 
 before_install:
   - 'gem install bundler'