Update the webpack config for production assets to gzip

[justin808]

For production deployment, we should gzip any assets. And only for production.

CC: @alexfedoseev

[justin808]

@alexfedoseev should we still do this?

[alex35mil]

@justin808 I thought pipeline handles this, no?

[justin808]

I'm pretty sure it can. I used to use the heroku deflater gem.

https://github.com/romanbsd/heroku-deflater

[alex35mil]

I remember I was investigating the things I need to do to replace AP and gzip was in the list that is handled by pipeline.