Fix iOS build after commit https://github.com/mono/CocosSharp/commit/872d9613cd741e3647b322a4a66225f6c57960fb
Fix iOS build after commit https://github.com/mono/CocosSharp/commit/872d9613cd741e3647b322a4a66225f6c57960fb

Issue #303

MSylvia/CocosSharp,mono/CocosSharp,mono/CocosSharp,MSylvia/CocosSharp