很久没更新Cocoapods版本，最近在项目有用Cocoapods管理私有库的需求，就更新了，遇到如下坑：
Cocoapods从0.39版本更新到1.2.0以后
运行报错：The dependency ......... is not used in any concrete target.
解决办法：Podfile文件需要指明使用的target，添加以下代码：
target '项目名' do
pod .....
解决后仍然报错：Invalid `Podfile` file: syntax error, unexpected end-of-input, expecting keyword_end.
解决办法：在Podfile的末尾添加 end
target '项目名' do
pod 公有库.....
pod '项目名',:git =>'https://github.com/........' //私有库
end
解决后继续报错：Oh no, an error occurred.
Search for existing GitHub issues similar to yours:https://github.com/CocoaPods/CocoaPods/search?q=undefined+method+%60dirname%27+for+nil%3ANilClass&type=Issues
If none exists, create a ticket, with the template displayed above, on:
https://github.com/CocoaPods/CocoaPods/issues/new
Be sure to first read the contributing guide for details on how to properly submit a ticket:
https://github.com/CocoaPods/CocoaPods/blob/master/CONTRIBUTING.md
解决办法：升级合并Cocoapods时产生了错误，删除重装
命令行：$ sudo rm -fr ~/.cocoapods/repos/master
$ pod setup
终于能用了....
