Always look at your traffic logs before making this kind of decision, but global usage is at 2.3%: https://caniuse.com/usage-table

I personally have dropped it for most of the apps I make (especially mobile web apps) so I can drastically reduce the final JavaScript bundle size by not having to polyfill a bunch of crap that all modern browsers already have built-in (Promises, fetch, fat arrow functions, let, const, etc.).