Log Message:
youtube-dl: Update to 20190511

Changes:
2019.05.11
----------
Core
* [utils] Transliterate "þ" as "th" (#20897)

Extractors
+ [cloudflarestream] Add support for videodelivery.net (#21049)
+ [byutv] Add support for DVR videos (#20574, #20676)
+ [gfycat] Add support for URLs with tags (#20696, #20731)
+ [openload] Add support for verystream.com (#20701, #20967)
* [youtube] Use sp field value for signature field name (#18841, #18927,
  #21028)
+ [yahoo:gyao] Extend URL regular expression (#21008)
* [youtube] Fix channel id extraction (#20982, #21003)
+ [sky] Add support for news.sky.com (#13055)
+ [youtube:entrylistbase] Retry on 5xx HTTP errors (#20965)
+ [francetvinfo] Extend video id extraction (#20619, #20740)
* [4tube] Update token hosts (#20918)
* [hotstar] Move to API v2 (#20931)
* [fox] Fix API error handling under python 2 (#20925)
+ [redbulltv] Extend URL regular expression (#20922)