While this site doesn't offer GIF conversion at the moment, you can
still do it yourself with the help of asciinema GIF generator utility - agg.
Once you have it installed run the following command to create GIF file:
agg https://asciinema.org/a/224221 224221.gif
Or, if you already downloaded the recording file:
agg 224221.cast 224221.gif
Check agg --help
for all available options. You can change font
family and size, select color theme, adjust speed and more.
See agg manual for
full usage instructions.