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 #42
Description
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.