I came across this while working on #90 .
Both GetDiff() and GetPatch() take an options parameter which is an object. Looking at the API here and here I think this parameter should be called spec and should just be a string; passing in a random object will cause errors.
In addition, GetDiff() should be able to take an object like ListParameters that provides context, path, ignore_whitespace, and binary.
I can put together a PR if you agree that these should be fixed.