devel/maven: update to 3.8.1

This is not just a bugfix as it contains three features that cause a change of
default behavior (external HTTP insecure URLs are now blocked by default): your
builds may fail when using this new Maven release, if you use now blocked
repositories. Please check and eventually fix before upgrading.

Changes http://maven.apache.org/docs/3.8.1/release-notes.html

PR:		255161
Approved by:	Jonathan Chen <jonc@chen.org.nz> (maintainer)
Security:	CVE-2021-26291
		CVE-2020-13956