Fix docstring of replace_datafile

[bpoldrack]

The identifier needed here is that of the to be replaced file, not an identifier of the dataset.

Despite the template suggesting, that the "project only accepts pull requests related to open issues", it seems a bit of an overkill for this kind of change to also open an issue. ;-)

[skasberger]

Update: I left AUSSDA, so my funding for pyDataverse development has stopped.

I want to get some basic funding to implement the most urgent updates (PRs, Bug fixes, maintenance work). If you can support this, please reach out to me. (www.stefankasberger.at). If you have feature requests, the same.

Another option would be, that someone else helps with the development and / or maintenance. For this, also get in touch with me (or comment here).

[shoeffner]

This change is also included in #202.

[bpoldrack]

Closing in favor of #202