Log Message:
youtube-dl: Update to 20190901

Changes:
2019.09.01
----------
Core
+ [extractor/generic] Add support for squarespace embeds (#21294, #21802,
  #21859)
+ [downloader/external] Respect mtime option for aria2c (#22242)

Extractors
+ [xhamster:user] Add support for user pages (#16330, #18454)
+ [xhamster] Add support for more domains
+ [verystream] Add support for woof.tube (#22217)
+ [dailymotion] Add support for lequipe.fr (#21328, #22152)
+ [openload] Add support for oload.vip (#22205)
+ [bbccouk] Extend URL regular expression (#19200)
+ [youtube] Add support for invidious.nixnet.xyz and yt.elukerio.org (#22223)
* [safari] Fix authentication (#22161, #22184)
* [usanetwork] Fix extraction (#22105)
+ [einthusan] Add support for einthusan.ca (#22171)
* [youtube] Improve unavailable message extraction (#22117)
+ [piksel] Extract subtitles (#20506)