Update browserslist to use @cfpb/browserslist-config stats

[anselmbradford]

I recommend using our shared browserslist package based on cf.gov browser metrics. The only reason not to do this is if this project has substantially different visitor browser metrics from consumerfinance.gov. If this is the case, you can still use the shared stats plus your own, such as > 0.2% in @cfpb/browserslist-config stats, Firefox >= 54

See updates to copy in https://github.com/cfpb/consumerfinance.gov/pull/8379/files