[!] Unable to find host target(s

pod install时报错：

[!] Unable to find host target(s) for IMSDK. Please add the host targets for the embedded targets to the Podfile.

Certain kinds of targets require a host target. A host target is a "parent" target which embeds a "child" target. These are example types of targets that need a host target:

- Framework

- App Extension

- Watch OS 1 Extension

- Messages Extension (except when used with a Messages Application)

解决方法，把pod降一个版本。