Fix type in CCLayer's public override void Visit.
Fix type in CCLayer's public override void Visit.

See issue https://github.com/mono/CocosSharp/issues/239

zmaruo/CocosSharp,mono/CocosSharp,haithemaraissia/CocosSharp,MSylvia/CocosSharp,zmaruo/CocosSharp,TukekeSoft/CocosSharp,mono/CocosSharp,TukekeSoft/CocosSharp,MSylvia/CocosSharp,haithemaraissia/CocosSharp