Fix typo in docs

[amiedes]

Proposed fixes:

Just fixes a typo

Features:

• includes tests covering changes
• includes updated documentation
• includes user-visible changes
• includes API changes
• includes bugfix for possible backport

Please [X] all the boxes above that apply

[amercader]

Thanks @amiedes you can name the file however you want as long as you reference it properly on setup.py, but I agree that plugin.py is more consistent with the rest of the docs and examples.