The sandbox is not in sync with the Podfile.lock

In our most recent update to the OS X build environment we updated the version of CocoaPods. This has resulted in some users experiencing a problem during their builds that looks like this:

 "❌ error: The sandbox is not in sync with the Podfile.lock. Run 'pod install' or update your CocoaPods installation. 

The best way to work around this issue is to add a step run run pod install in circle.yml like this:

    - bundle install
    - bundle exec pod install

This will update all of your pods, which will be cached in the future and this error will no longer occur.