警告内容：
[!] Automatically assigning platform `ios` with version `11.4` on target `XXXXXX` because no platform was specified. Please specify a platform for this target in your Podfile. See `https://guides.cocoapods.org/syntax/podfile.html#platform`.
产生原因：
在Podfile中未指定target的平台platform。
解决办法：
指定平台platform
platform :ios, ‘4.0’
platform :ios