今天更新CocoaPads的时候突然遇到以下问题，而且感觉pch文件一下子不管用了，在此记录一下：

[!] CocoaPods could not find compatible versions for pod "MJRefresh":
  In snapshot (Podfile.lock):
    MJRefresh (= 3.1.15.3)

  In Podfile:
    MJRefresh

None of your spec sources contain a spec satisfying the dependencies: `MJRefresh, MJRefresh (= 3.1.15.3)`.

You have either:
 * out-of-date source repos which you can update with `pod repo update` or with `pod install --repo-update`.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.

解决方法：把.xcworkspace和Podfile.lock文件删除，重新pod install一下就好了！