Log Message:
youtube-dl: Update to 20210606

Changes:
20210606
--------
Extractors
* [facebook] Improve login required detection
* [youporn] Fix formats and view count extraction (#29216)
* [orf:tvthek] Fix thumbnails extraction (#29217)
* [formula1] Fix extraction (#29206)
* [ard] Relax URL regular expression and fix video ids (#22724, #29091)
+ [ustream] Detect https embeds (#29133)
* [ted] Prefer own formats over external sources (#29142)
* [twitch:clips] Improve extraction (#29149)
+ [twitch:clips] Add access token query to download URLs (#29136)
* [youtube] Fix get_video_info request (#29086, #29165)
* [vimeo] Fix vimeo pro embed extraction (#29126)
* [redbulltv] Fix embed data extraction (#28770)
* [shahid] Relax URL regular expression (#28772, #28930)

20210516
--------
Core
* [options] Fix thumbnail option group name (#29042)
* [YoutubeDL] Improve extract_info doc (#28946)

Extractors
+ [playstuff] Add support for play.stuff.co.nz (#28901, #28931)
* [eroprofile] Fix extraction (#23200, #23626, #29008)
+ [vivo] Add support for vivo.st (#29009)
+ [generic] Add support for og:audio (#28311, #29015)
* [phoenix] Fix extraction (#29057)
+ [generic] Add support for sibnet embeds
+ [vk] Add support for sibnet embeds (#9500)
+ [generic] Add Referer header for direct videojs download URLs (#2879,
  #20217, #29053)
* [orf:radio] Switch download URLs to HTTPS (#29012, #29046)
- [blinkx] Remove extractor (#28941)
* [medaltv] Relax URL regular expression (#28884)
+ [funimation] Add support for optional lang code in URLs (#28950)
+ [gdcvault] Add support for HTML5 videos
* [dispeak] Improve FLV extraction (#13513, #28970)
* [kaltura] Improve iframe extraction (#28969)
* [kaltura] Make embed code alternatives actually work
* [cda] Improve extraction (#28709, #28937)
* [twitter] Improve formats extraction from vmap URL (#28909)
* [xtube] Fix formats extraction (#28870)
* [svtplay] Improve extraction (#28507, #28876)
* [tv2dk] Fix extraction (#28888)