build(percy): Fix percy rendering w/ emotion

[billyvg]

emotion doesn't render styles into DOM when NODE_ENV == production, so add logic to do this when we are in a percy environment

• - deploy and test on staging

[MaxBittker]

this is definitely a runtime check right? because travis builds the bundles. so prepack or whatever could accidently trigger this (very theoretical)
it would be nice to have a foolproof way to be sure this doesn't end up in prod silently ;/
Any thoughts?

[billyvg]

Travis doesn't build our bundles when we deploy. This is really a build-time check because process.env gets injected by webpack.

Unrelated but we should wrap the code in a condition block so it gets minified away in prod.