failes ffmpeg url about octoprint-docker

[fionnb]

The new, correct URL is:
https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-armel-static.tar.xz

It is just a matter of replacing it in the Dockerfile.

[Cthanatos]

Well, until it gets fixed - here's what I did. (use at your own risk, as SSL certs are important for a reason)

• Get into the shell of your docker as root user with
  docker exec -u 0 -it organizr /bin/bash

• change to tmp directory
  cd /tmp/

• Use wget to get the file, but you have to ignore the certificate issues ( You'll get warnings, but it still downloads)
  wget --no-check-certificate -O ffmpeg.tar.xz https://johnvansickle.com/ffmpeg/releases/ffmpeg-release-32bit-static.tar.xz

• Make the directory before unzipping the tar
  mkdir -p /opt/ffmpeg

• Untar to the right location
  tar xvf ffmpeg.tar.xz -C /opt/ffmpeg --strip-components=1

• Remove ffmpeg download file
  rm -Rf /tmp/*

• Set right location in webUI when setting up for ffmpeg
  /opt/ffmpeg/ffmpeg