pod 创建自定义库失败后解决方案

遇到以上问题：

Cloning `https://github.com/CocoaPods/pod-template.git` into `GlobalButton`.

Configuring GlobalButton template.

Ignoring ffi-1.15.5 because its extensions are not built. Try: gem pristine ffi --version 1.15.5

/Library/Ruby/Site/2.6.0/rubygems/specification.rb:1458:in `rescue in block in activate_dependencies': Could not find 'rexml' (~> 3.2.4) among 38 total gem(s) (Gem::MissingSpecError)
。。。。。。。。。。。。。此处省略中间部分

To learn more about the template see `https://github.com/CocoaPods/pod-template.git`.

To learn more about creating a new pod, see `https://guides.cocoapods.org/making/making-a-cocoapod`.
解决方案：
gem install --user-install rexml
gem install --user-install xcodeproj
执行pod lib create GlobalButton，运行成功。