fix typo in nbinom distribution

[saraloo]

Describe your changes.

This pull request edits a small typo to allow the nbinom likelihood to work within calibration.

Does this pull request make any user interface changes? If so please describe.

None, just the config syntax would look something like

      likelihood:
        dist: nbinom
        params:
          alpha: 0.3

[pearsonca]

@saraloo at this point, anything you want to do w/ flepimop is entirely your call.

@TimothyWillard - should we deactivate e.g. review rules for merging etc?

Should also update something here to explain that flepimop is now in minimal maintenance mode

[TimothyWillard]

@saraloo at this point, anything you want to do w/ flepimop is entirely your call.

@TimothyWillard - should we deactivate e.g. review rules for merging etc?

Should also update something here to explain that flepimop is now in minimal maintenance mode

I think that seems reasonable. I can add the PR for the note to the README.md today, but I do not have permissions to change the review rules.