travis-ci/update-git.sh: add --gem-cache option
travis-ci/update-git.sh: add --gem-cache option

dirkmueller/crowbar,toabctl/crowbar,rhafer/crowbar,mmnelemane/crowbar,SUSE-Cloud/crowbar,aplanas/crowbar,rhafer/crowbar,aplanas/crowbar,toabctl/crowbar,rsalevsky/crowbar,aspiers/crowbar,tserong/crowbar,rsalevsky/crowbar,MaximilianMeister/crowbar,SUSE-Cloud/crowbar,vwallfahrer/crowbar,aspiers/crowbar,nkrinner/crowbar,dirkmueller/crowbar,MaximilianMeister/crowbar,tserong/crowbar,nkrinner/crowbar,crowbar/crowbar,crowbar/crowbar,vwallfahrer/crowbar,rhafer/crowbar,mmnelemane/crowbar