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。
