平常使用pod的时候，会有很多错误，在此准备把遇到的错误，逐一写出来，以供查找：

[!] Unable to satisfy the following requirements:

- `CYLTabBarController` required by `Podfile`
- `CYLTabBarController (= 1.14.1)` required by `Podfile.lock`

None of your spec sources contain a spec satisfying the dependencies: `CYLTabBarController, CYLTabBarController (= 1.14.1)`.

You have either:
 * out-of-date source repos which you can update with `pod repo update`.
 * mistyped the name or version.
 * not added the source repo that hosts the Podspec to your Podfile.

Note: as of CocoaPods 1.0, `pod repo update` does not happen on `pod install` by default.

这个错误是因为所引用的库，已经有了更新，而Podfile文件并没有更改其下载版本（Podfile文件过期），我们需要update一下

[dayaodeMacBook-Pro:dayao$ pod update
Update all pods
Updating local specs repositories

更新时间比较长，请耐心等待，更新完成之后，就可以用了