传入的contentView使用xib layout 布局时内容撑不开（例：多行UILabel不会自动撑开，需要设置准确的contentView高度才可以）这种情况怎么设置

[RS-Li]

New Issue Checklist

• I have read and understood the CONTRIBUTING guide
• I have searched for a similar issue in the project and found none

Issue Info

Info	Value
Platform Name	e.g. ios
Platform Version	e.g. 11.0 / 12.1.2
FFPopup Version	e.g. 1.0.0
Integration Method	e.g. carthage / cocoapods / manually
Xcode Version	e.g. Xcode 10.1
Repro rate	e.g. all the time (100%) / sometimes x% / only once
Repro with our demo prj	e.g. does it happen with our demo project?
Demo project link	e.g. link to a demo project that highlights the issue

Issue Description and Steps

Please fill in the detailed description of the issue (full output of any stack trace, compiler error, ...) and the steps to reproduce the issue.