title: CocoaPods - use specific pod version
body: <p>I am using CocoaPods for a macOS app. I have compilation errors with AFNetworking (current version, 1.2.1) and saw that these didn't exist in the previous version (1.2.0). </p>
  
  <p>I did some research but did not find a possibility to define the version of a pod (for example, version 1.2.0 instead of 1.2.1).</p>
  
  <p>Is this possible or do I have to wait until there is a new version of that library?</p>