Add Rails 5.0 and 5.1 on jruby to allowed failures

The jdbc adapters arent working with the latest patch releases of Rails.
We'd like to test these if they could work, so I've added them to
allowed_failures instead of fully excluding them.

.travis.yml

@@ -43,6 +43,11 @@ matrix:
       gemfile: gemfiles/Gemfile.rails-4.0.rb
     - rvm: 2.4.0
       gemfile: gemfiles/Gemfile.rails-4.1.rb
+  allow_failures:
+    - rvm: jruby-9.1.13.0
+      gemfile: gemfiles/Gemfile.rails-5.1.rb
+    - rvm: jruby-9.1.13.0
+      gemfile: gemfiles/Gemfile.rails-5.0.rb
 
 sudo: false