only install unzipper on windows

[dradetsky]

currently, we install unzipper unconditionally, even though it's only required by the window, which causes a lot of unnecessary installs to node_modules/beamcoder/node_modules. Additionally, we also depend on it, which causes those same dependencies to also be added to my project, but i think not actually made available to the beamcoder install process if it needs them. This leads to a significant increase in disk usage by programs using beamcoder.

To fix this, we only actually install unzipper inside the windows installer, and only load it near the call site.

FWIW, a better direction for the future might be to factor install_ffmpeg.js out into a separate package. You could make it a peer dependency, or just catch ffmpeg-not-found type errors and print "try installing beamcoder-install-ffmpeg".

[scriptorian]

Thanks for this. I have updated the head revision so will now close this pull request.