fix condition to set yaml engine

* test/rubygems/test_gem_specification.rb (test_to_yaml_emits_syck_compat_yaml):
  fix condition to set yaml engine.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@35450 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/rubygems/test_gem_specification.rb

@@ -1209,7 +1209,7 @@ end
   end
 
   def test_to_yaml_emits_syck_compat_yaml
-    if YAML.const_defined?(:ENGINE) && !YAML::ENGINE.syck?
+    if YAML.const_defined?(:ENGINE) && YAML::ENGINE.syck?
       yamler, YAML::ENGINE.yamler = YAML::ENGINE.yamler, 'psych'
     end
     begin