Disable failing activerecord tests on ruby 2.5.0

These tests are already fixed on 5-1-stable.
rails/rails@0806941

Rakefile

@@ -104,6 +104,27 @@ namespace :turntable do
             EOS
           end
         end
+
+        if ActiveRecord.gem_version.release <= Gem::Version.new("5.1.4")
+          ignores = [
+            ["aggregations_test.rb", "AggregationsTest", "test_immutable_value_objects"],
+            ["query_cache_test.rb",  "QueryCacheTest", "test_query_cache_does_not_allow_sql_key_mutation"],
+            ["transactions_test.rb", "TransactionTest", "test_rollback_when_saving_a_frozen_record"],
+          ]
+
+          ignores.each do |file_name, class_name, method_name|
+            path = File.join("test/cases", file_name)
+            next unless File.exist?(path)
+
+            File.open(File.join("test/cases", file_name), "a") do |f|
+              f << <<-EOS.strip_heredoc
+                class #{class_name}
+                  undef_method :#{method_name} if method_defined?(:#{method_name})
+                end
+              EOS
+            end
+          end
+        end
       end
 
       task :db => :rails do