youtube-dl should integrate a recent a upstream patch that fixes downloading .mp4/.gifs from Twitter

When attempting to download a .gif files from Twitter (which are actually .mp4 files, but Twitter calls them .gifs anyway) using youtube-dl, it errors-out as follows:

---- SNIP -----
youtube-dl https://twitter.com/TWITTER_USER/status/XXXXXXXXXXXXXXXXX

[twitter] XXXXXXXXXXXXXXXXX: Downloading webpage
[twitter:card] XXXXXXXXXXXXXXXXX: Downloading webpage
ERROR: No video formats found; please report this issue on https://yt-dl.org/bug . Make sure you are using the latest version; see https://yt-dl.org/update on how to update. Be sure to call youtube-dl with the --verbose flag and include its complete output.
----- /SNIP -----

However, upstream has fixed this issue recently, and their commit can be found here:

https://github.com/rg3/youtube-dl/commit/b6b2ccb72fb7da7563078d4bf047d1622ba89553

Replacing ``/usr/lib/python3/dist-packages/youtube_dl/extractor/twitter.py`` with the updated version from the above commit was enough to get youtube-dl to successfully start downloading .gif/.mp4s from Twitter, so it should be easy to backport.

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: youtube-dl 2018.03.14-1
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair nvidia_modeset nvidia
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Jul 3 13:27:33 2018
InstallationDate: Installed on 2018-06-16 (17 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
SourcePackage: youtube-dl
UpgradeStatus: No upgrade log present (probably fresh install)