[twitter] Allow single dash to be used as username

[Lesmiscore]

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• Bug fix
• Improvement
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Description of your pull request and other information

This PR allows to use single dash for username part in video tweet urls.
Taking follwing command as an example,

youtube-dl --output="%(uploader_id).%(ext)" https://twitter.com/-/status/1087791357756956680?s=19

youtube-dl used to save this video in a file named -.mp4, with this PR saved video will be named like twitter.mp4.