It works fine. You need some correct file id and revision id.
For eg -
File Id = 0Vs336aBx5r3MdHJz1TZaCi1kb0JsOExoSHJDMWFZVUE
Revision Id = 13723331213000
Steps -
Get a valid File Id from here. In try it out - maxResults = 5 https://developers.google.com/drive/v2/reference/files/list
From the json reply select any file id.Get all the revisions for this file - https://developers.google.com/drive/v2/reference/revisions/list
Try it out - fieldId = enter the File Id copied from above step.
From the json reply select any revision idNow use the File Id and Revision Id here - https://developers.google.com/drive/v2/reference/revisions/get#try-it