Fix docstrings

[RondeauG]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
• (If applicable) Tests have been added.
• This PR does not seem to break the templates.
• HISTORY.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• Fix for when a single period is called in produce_horizon.
• Fix between dask and compute_indicators when asking for warming levels in produce_horizon

Does this PR introduce a breaking change?

Other information:

[juliettelavoie]

toute une ride cette PR qui commençait simplement par typo_fix! :P