我将我的Xcode升级到版本7，突然出现以下错误:Sep2415:44:31LogoSwift[10211]:CGContextSaveGState:invalidcontext0x0.Ifyouwanttoseethebacktrace,pleasesetCG_CONTEXT_SHOW_BACKTRACEenvironmentalvariable.Sep2415:44:31LogoSwift[10211]:CGContextTranslateCTM:invalidcontext0x0.Ifyouwanttoseethebacktrace,pleasesetCG_CONTEXT_SHO