Command PhaseScriptExecution failed with a nonzero exit code
解决方法：
第一种：xcode菜单file->Workspace Settings->Build System 选择Legacy Build System 使用旧的编译系统即可。
第二种：sudo gem install cocoapods --pre
pod update
升级cocoapods到1.6.0beta，参考：cocoapods - Xcode 10 Command PhaseScriptExecution failed with a nonzero exit code (EXPANDED_CODE_SIGN_IDENTITY: unbound variable) - Stack Overflow
