Log Message:
youtube-dl: update to latest version (2018.05.18)

Commit shortlog:
[itv] Improve extraction (closes #16253)
[tunein] Use live title for live streams (closes #16347)
Improve geo bypass mechanism * Introduce geo bypass context * Add ability to \ 
bypass based on IP blocks in CIDR notation * Introduce --geo-bypass-ip-block
[itv:btcc] Add extractor (closes #16139)
[watchbox] Fix extraction (closes #16356)
[cloudflarestream] Add support for cloudflare streams (closes #16375)
[businessinsider] Add extractor (closes #16387, closes #16388, closes #16389)
[udemy] Extract stream URLs (closes #16372)
[udemy] Extract asset captions
[YoutubeDL] Ensure ext exists for automatic captions
[ChangeLog] Actualize [ci skip]
release 2018.05.09
[nickbr] Relax _VALID_URL (#13230)
[mixcloud] Bypass throttling for HTTP formats (#12579, #16424)
[twitch:clips] Fix extraction (closes #16429)
[twitch:clips] Sort formats
[youtube] Make uploader extraction non fatal (#16444)
[youtube] Improve format filesize extraction (#16453)
[options] Fix typo (closes #16450)
[vimeo:likes] Relax _VALID_URL and fix single page likes extraction (closes #16475)
[ChangeLog] Actualize [ci skip]
release 2018.05.18