Incorrect documentation regarding errors during files_batch* requests #111

Hey there,

We're using files_move_batch and files_move_batch_check. Talking to support, they've acknowledge that transient errors can occur during either of these two calls requiring a nominal back-off retry. While try/excepting these conditions, the documentation says that ApiError.reason carries the domain-specific error and in our case the error would be dropbox.files.PollError.

Neither of these cases are accurate: ApiError.error contains the error (there is no 'reason' member) and dropbox.async.PollError was returned, not dropbox.files.PollError.

We're using dropbox 7.2.1 but I've just checked 7.3.1 docs and the inconsistency remains:

If this raises, ApiError.reason is of type:
dropbox.files.PollError