古いUnityのPluginでTargetGuidByNameエラーが出たら

Exception: Calling TargetGuidByName with name='Unity-iPhone' is deprecated. There are two targets now, call GetUnityMainTargetGuid() - for app or GetUnityFrameworkTargetGuid() - for source/plugins to get Guid instead.

proj.TargetGuidByName("Unity-iPhone");

↓

proj.GetUnityMainTargetGuid();