[Snyk] Upgrade @primer/css from 15.1.0 to 15.2.0#3

snyk-bot wants to merge 1 commit intomainRanaAhmed2020/docs:mainfrom

snyk-upgrade-60508e94e7d01d7c1dfa163e5e4f72eeRanaAhmed2020/docs:snyk-upgrade-60508e94e7d01d7c1dfa163e5e4f72eeCopy head branch name to clipboard