[imgur] doesn't support short video ids

[jwilk]

$ youtube-dl -v https://i.imgur.com/Ku6I4.gifv
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'https://i.imgur.com/Ku6I4.gifv']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2016.04.06
[debug] Python version 2.7.11+ - Linux-4.3.0-1-amd64-x86_64-with-debian-stretch-sid
[debug] exe versions: none
[debug] Proxy map: {}
[generic] Ku6I4: Requesting header
WARNING: Falling back on generic information extractor.
[generic] Ku6I4: Downloading webpage
[generic] Ku6I4: Extracting information
[debug] Invoking downloader on u'https://i.imgur.com/Ku6I4.webm'
[download] Destination: ♫ Brusha, Brusha, Brusha ♫ Get the new Ipana ♫ With the brand new flavor ♫ Its dandy for your teeth-Ku6I4.webm
[download] 389.0% of 1.72KiB at 566.41KiB/s ETA 00:00ERROR: content too short (expected 1763 bytes and served 6858)
Traceback (most recent call last):
  File "/home/jwilk/.local/lib/python2.7/site-packages/youtube_dl/YoutubeDL.py", line 1633, in process_info
    success = dl(filename, info_dict)
  File "/home/jwilk/.local/lib/python2.7/site-packages/youtube_dl/YoutubeDL.py", line 1575, in dl
    return fd.download(name, info)
  File "/home/jwilk/.local/lib/python2.7/site-packages/youtube_dl/downloader/common.py", line 350, in download
    return self.real_download(filename, info_dict)
  File "/home/jwilk/.local/lib/python2.7/site-packages/youtube_dl/downloader/http.py", line 236, in real_download
    raise ContentTooShortError(byte_counter, int(data_len))
ContentTooShortError

Apparently that's because the imgur extractor assumes that the video is at least 6 characters long, but it's only 5 characters in this case.