Upgrade Ruby 2.2 tests to 2.3

This changes the GitLab CI Tests that test compatibility with Ruby 2.2
to instead test compat with Ruby 2.3.

We’ve discussed skipping straight to 2.3.0 when next upgrading the
required Ruby version.

Since Rails 5 requires 2.2.2, and we have to upgrade anyway, may as
well do it now and not risk having to upgrade again come Rails 5.1 or
5.2.

Test failures on Ruby 2.3 do not fail the build.

.gitlab-ci.yml

@@ -129,56 +129,51 @@ spinach 7 10: *spinach-knapsack
 spinach 8 10: *spinach-knapsack
 spinach 9 10: *spinach-knapsack
 
-# Execute all testing suites against Ruby 2.2
-
-.ruby-22: &ruby-22
-  image: "ruby:2.2"
+# Execute all testing suites against Ruby 2.3
+.ruby-23: &ruby-23
+  image: "ruby:2.3"
   only:
     - master
-  cache:
-    key: "ruby22"
-    paths:
-    - vendor
 
-.rspec-knapsack-ruby22: &rspec-knapsack-ruby22
+.rspec-knapsack-ruby23: &rspec-knapsack-ruby23
   <<: *rspec-knapsack
-  <<: *ruby-22
+  <<: *ruby-23
 
-.spinach-knapsack-ruby22: &spinach-knapsack-ruby22
+.spinach-knapsack-ruby23: &spinach-knapsack-ruby23
   <<: *spinach-knapsack
-  <<: *ruby-22
+  <<: *ruby-23
   
-rspec 0 20 ruby22: *rspec-knapsack-ruby22
-rspec 1 20 ruby22: *rspec-knapsack-ruby22
-rspec 2 20 ruby22: *rspec-knapsack-ruby22
-rspec 3 20 ruby22: *rspec-knapsack-ruby22
-rspec 4 20 ruby22: *rspec-knapsack-ruby22
-rspec 5 20 ruby22: *rspec-knapsack-ruby22
-rspec 6 20 ruby22: *rspec-knapsack-ruby22
-rspec 7 20 ruby22: *rspec-knapsack-ruby22
-rspec 8 20 ruby22: *rspec-knapsack-ruby22
-rspec 9 20 ruby22: *rspec-knapsack-ruby22
-rspec 10 20 ruby22: *rspec-knapsack-ruby22
-rspec 11 20 ruby22: *rspec-knapsack-ruby22
-rspec 12 20 ruby22: *rspec-knapsack-ruby22
-rspec 13 20 ruby22: *rspec-knapsack-ruby22
-rspec 14 20 ruby22: *rspec-knapsack-ruby22
-rspec 15 20 ruby22: *rspec-knapsack-ruby22
-rspec 16 20 ruby22: *rspec-knapsack-ruby22
-rspec 17 20 ruby22: *rspec-knapsack-ruby22
-rspec 18 20 ruby22: *rspec-knapsack-ruby22
-rspec 19 20 ruby22: *rspec-knapsack-ruby22
-
-spinach 0 10 ruby22: *spinach-knapsack-ruby22
-spinach 1 10 ruby22: *spinach-knapsack-ruby22
-spinach 2 10 ruby22: *spinach-knapsack-ruby22
-spinach 3 10 ruby22: *spinach-knapsack-ruby22
-spinach 4 10 ruby22: *spinach-knapsack-ruby22
-spinach 5 10 ruby22: *spinach-knapsack-ruby22
-spinach 6 10 ruby22: *spinach-knapsack-ruby22
-spinach 7 10 ruby22: *spinach-knapsack-ruby22
-spinach 8 10 ruby22: *spinach-knapsack-ruby22
-spinach 9 10 ruby22: *spinach-knapsack-ruby22
+rspec 0 20 ruby23: *rspec-knapsack-ruby23
+rspec 1 20 ruby23: *rspec-knapsack-ruby23
+rspec 2 20 ruby23: *rspec-knapsack-ruby23
+rspec 3 20 ruby23: *rspec-knapsack-ruby23
+rspec 4 20 ruby23: *rspec-knapsack-ruby23
+rspec 5 20 ruby23: *rspec-knapsack-ruby23
+rspec 6 20 ruby23: *rspec-knapsack-ruby23
+rspec 7 20 ruby23: *rspec-knapsack-ruby23
+rspec 8 20 ruby23: *rspec-knapsack-ruby23
+rspec 9 20 ruby23: *rspec-knapsack-ruby23
+rspec 10 20 ruby23: *rspec-knapsack-ruby23
+rspec 11 20 ruby23: *rspec-knapsack-ruby23
+rspec 12 20 ruby23: *rspec-knapsack-ruby23
+rspec 13 20 ruby23: *rspec-knapsack-ruby23
+rspec 14 20 ruby23: *rspec-knapsack-ruby23
+rspec 15 20 ruby23: *rspec-knapsack-ruby23
+rspec 16 20 ruby23: *rspec-knapsack-ruby23
+rspec 17 20 ruby23: *rspec-knapsack-ruby23
+rspec 18 20 ruby23: *rspec-knapsack-ruby23
+rspec 19 20 ruby23: *rspec-knapsack-ruby23
+
+spinach 0 10 ruby23: *spinach-knapsack-ruby23
+spinach 1 10 ruby23: *spinach-knapsack-ruby23
+spinach 2 10 ruby23: *spinach-knapsack-ruby23
+spinach 3 10 ruby23: *spinach-knapsack-ruby23
+spinach 4 10 ruby23: *spinach-knapsack-ruby23
+spinach 5 10 ruby23: *spinach-knapsack-ruby23
+spinach 6 10 ruby23: *spinach-knapsack-ruby23
+spinach 7 10 ruby23: *spinach-knapsack-ruby23
+spinach 8 10 ruby23: *spinach-knapsack-ruby23
+spinach 9 10 ruby23: *spinach-knapsack-ruby23
 
 # Other generic tests