Update test description

Author: causztic

spec/integration/composite_primary_key_spec.rb

@@ -26,7 +26,7 @@
     end
   end
 
-  context "without composite_primary_key, searching against association with a composite_primary_key" do
+  context "searching against relation with a composite_primary_key" do
     with_model :Parent do
       table primary_key: [:first_name, :last_name] do |t|
         t.string :first_name