Upgrade split2@4

[perrin4869]

split2@3 depends on readable-stream, which is notorious for being difficult to bundle with rollup due to a circular dependency. Version 4 does away with this dependency and uses the core node stream library instead (and bumps the minimum node version to v12).
I hope this simplifies bundling node-postgres with rollup

[hoegaarden]

Thanks, @perrin4869 !

Your PR has been merged and the new version of pgpass has been published.

[perrin4869]

Thanks @hoegaarden!
Node 10 still works, but it isn't formally supported by split2 V4... So I was wondering if it would be safer to publish this as a major release instead, dropping node 10 and adding 16 :)