Fix typo in README file.
Fix typo in README file.

smerrill/packer,suma/packer,patricklucas/packer,suma/packer,zyegfryed/packer,patricklucas/packer,Kaixiang/packer,TranscendComputing/packer,smerrill/packer,suma/packer,patricklucas/packer,TranscendComputing/packer,smerrill/packer,patricklucas/packer,suma/packer,zyegfryed/packer,smerrill/packer,Kaixiang/packer,TranscendComputing/packer,Kaixiang/packer,Kaixiang/packer,TranscendComputing/packer,zyegfryed/packer,zyegfryed/packer