This disables sourcemap generation for production builds to save on
disk space. While useful, source maps are several times larger than
our actual used code, so it's best to only keep them around during
development.
This also turns off gzip, since it is just duplicating files for now;
we'll want to reconsider this feature once StackViz is building inside
the gate if links start breaking.
Change-Id: Ie4c2735c08014f417b8f1f68fc8f6b9e4898dff2
d2e9ad4fca