Get请求中，带有汉字，转成UTF-8

• 9.0以前

NSString *urlSreing = @"www.baidu.com";
NSString *unicodeStr = (NSString *)CFBridgingRelease(CFURLCreateStringByAddingPercentEscapes(NULL, (CFStringRef)urlString, NULL, NULL, kCFStringEncodingUTF8));

• 9.0开始

NSString *unicodeStr = [urlString stringByAddingPercentEncodingWithAllowedCharacters:NSCharacterSet.URLQueryAllowedCharacterSet];