www/node12: Update 12.20.2 -> 12.21.0

https://nodejs.org/en/blog/release/v12.21.0/

This is a security release. See
https://nodejs.org/en/blog/vulnerability/february-2021-security-releases/

While here, pet portlint by moving USES.

PR: 254043
Submitted by: jlduran@gmail.com
MFH: 2021Q1
Security: 2f3cd69e-7dee-11eb-b92e-0022489ad614
Sponsored by: Miles AS