Log Message:
youtube-dl: Update net/youtube-dl to 20181209

Changes:
2018.12.09
----------
Core
* [YoutubeDL] Keep session cookies in cookie file between runs
* [YoutubeDL] Recognize session cookies with expired set to 0 (#12929)

Extractors
+ [teachable] Add support for teachable platform sites (#5451, #18150, #18272)
+ [aenetworks] Add support for historyvault.com (#18460)
* [imgur] Improve gallery and album detection and extraction (#9133, #16577,
  #17223, #18404)
* [iprima] Relax URL regular expression (#18453)
* [hotstar] Fix video data extraction (#18386)
* [ard:mediathek] Fix title and description extraction (#18349, #18371)
* [xvideos] Switch to HTTPS (#18422, #18427)
+ [lecturio] Add support for lecturio.com (#18405)
+ [nrktv:series] Add support for extra materials
* [nrktv:season,series] Fix extraction (#17159, #17258)
* [nrktv] Relax URL regular expression (#18304, #18387)
* [yourporn] Fix extraction (#18424, #18425)
* [tbs] Fix info extraction (#18403)
+ [gamespot] Add support for review URLs