Fix file_spec of freebsd for serverspec v2
Fix file_spec of freebsd for serverspec v2

Use `stat -f` instead of `stat -c`

lurdan/specinfra,stefanhorning/specinfra,sergueik/specinfra,verisign/specinfra,serverspec/specinfra,mactkg/specinfra,miketheman/specinfra,electrical/specinfra,seroron/specinfra,r7kamura/specinfra,sorah/specinfra,nurse/specinfra,ihassin/specinfra,k0kubun/specinfra,chef-partners/specinfra-cisco,sean-horn/specinfra,minimum2scp/specinfra,bodgit/specinfra,uroesch/specinfra,mizzy/specinfra,hfm/specinfra,gh2k/specinfra,stoned/specinfra,chorrell/specinfra,elibus/specinfra,RoboticCheese/specinfra,chinthakagodawita/specinfra,winebarrel/specinfra,optimizely/specinfra,skamithi/specinfra,glenux/contrib-specinfra,tacahilo/specinfra,hideyuki/specinfra,higanworks/specinfra,thenexus6/specinfra,aibou/specinfra,pfaffle/specinfra,edolnx/specinfra