Cocoapods 报警告Automatically assigning platform ios with version 9.0 on target....

Automatically assigning platform iOS with version 9.0 on target 你的工程名称 because no platform was specified. Please specify a platform for this target in your Podfile. See `https://guides.cocoapods.org/syntax/podfile.html#platform`

这是在使用cocoapods安装三方库配置podfile之后的一个警告信息。