Exclude Rails 5.2.x/Ruby 2.2 from build matrix

Rails 5.2 has an unreleased fix for the use of the &. operator.

Author: pixeltrix

.travis.yml

@@ -102,6 +102,8 @@ matrix:
       rvm: 2.0.0
     - gemfile: gemfiles/Gemfile.rails-5.2.x
       rvm: 2.1.10
+    - gemfile: gemfiles/Gemfile.rails-5.2.x
+      rvm: 2.2.10
     - gemfile: gemfiles/Gemfile.rails-5.2.x.sprockets-4.x
       rvm: 1.9.3
     - gemfile: gemfiles/Gemfile.rails-5.2.x.sprockets-4.x