Fix for crossSbtVersions triggering lintBuild
Fix for crossSbtVersions triggering lintBuild

Currently crossSbtVersions is incorrectly generating a warning that it
is an unused setting (see https://github.com/sbt/sbt/pull/5153). This
PR fixes this by adding it to the list of excluded lint keys.

Fixes #6571.

mdedetrich/sbt,xuwei-k/xsbt,sbt/sbt,mdedetrich/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,sbt/sbt,xuwei-k/xsbt,mdedetrich/sbt,xuwei-k/xsbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,xuwei-k/xsbt,sbt/sbt,xuwei-k/xsbt,mdedetrich/sbt