Update browser support to match for at least 1 year

[scurker]

Our current .browserslistrc currently sets support to chrome 55 and firefox 54, which were initially released in 2016 and 2017 respectively. It's somewhat unreasonable to support almost 8+ year old browsers, especially considering most browser vendors push auto updates on a semi-regular basis.

We should instead move to a rolling model of setting our minimum browser support to only officially include browsers released within the past year or above a minimum threshhold, updating our .browserslistrc to the following:

> 1% or last 1 year
last 2 safari versions

Unofficially, we can make this the new policy going forward but cannot fully implement the change for .browserslistrc until the deprecation period has passed.