Fix "sort_link with hide order indicator" spec to fail properly

This regression test, added in #473, tested the presence of the
attribute name instead of the absence of the order indicators and would
never fail.

Josh Hunter / Jon Atack.

spec/ransack/helpers/form_helper_spec.rb

@@ -339,6 +339,7 @@ module Ransack
           )
         }
         it { should match /Full Name/ }
+        it { should_not match /▼|▲/ }
       end
 
       describe '#sort_link with hide order indicator set to false' do