Remove use of Dir.mktmpdir to get build to pass on JRuby.
Remove use of Dir.mktmpdir to get build to pass on JRuby.

The travis JRuby builds are intermittently failing with "permission denied" errors from `Dir.mktmpdir`.
Shopify/vcr,ZmagoD/vcr,Shopify/vcr,ZmagoD/vcr,irfanah/vcr,nishanbose/vcr,chriswoodrich/vcr,cemo/vcr,allyapp/vcr,myronmarston/vcr,davidbebb/vcr,mcfiredrill/vcr,davidbebb/vcr,nishanbose/vcr,intfrr/vcr,asymmetric/vcr,mcfiredrill/vcr,ihassin/vcr,intfrr/vcr,asymmetric/vcr,myronmarston/vcr,ihassin/vcr,cemo/vcr,allyapp/vcr,chriswoodrich/vcr,irfanah/vcr