[BUG] Incorrect year in footer

[darigovresearch]

Description of bug / unexpected behavior

Year is 2020 in the footer of the docs.

Expected behavior

It should be 2021

How to reproduce the issue

Go to any page in the docs
https://docs.manim.community/en/stable/examples.html

Additional media files

Logs

N/A

System specifications

N/A

Additional comments

N/A

[darigovresearch]

Pull request #1710 resolves this issue