Update youtube-dl to 2020.12.7

[pyup-bot]

This PR updates youtube-dl from 2020.12.5 to 2020.12.7.

Changelog

2020.12.07

Core
* [extractor/common] Extract timestamp from Last-Modified header
+ [extractor/common] Add support for dl8-* media tags (27283)
* [extractor/common] Fix media type extraction for HTML5 media tags
in start/end form

Extractors
* [aenetworks] Fix extraction (23363, 23390, 26795, 26985)
 * Fix Fastly format extraction
 + Add support for play and watch subdomains
 + Extract series metadata
* [youtube] Improve youtu.be extraction in non-existing playlists (27324)
+ [generic] Extract RSS video description, timestamp and itunes metadata
(27177)
* [nrk] Reduce the number of instalments and episodes requests
* [nrk] Improve extraction
 * Improve format extraction for old akamai formats
 + Add is_live value to entry info dict
 * Request instalments only when available
 * Fix skole extraction
+ [peertube] Extract fps
+ [peertube] Recognize audio-only formats (27295)

Links

• PyPI: https://pypi.org/project/youtube-dl
• Changelog: https://pyup.io/changelogs/youtube-dl/
• Repo: https://github.com/ytdl-org/youtube-dl

Resolves #2526