Fix to work with http chef_omnibus_url

Often people will reference getchef.com with http rather then https
for either using proxy caching software or due to The Enterprise
SSL proxy.  This allows the chef_omnibus_url to properly be updated
from .sh to .msi when referenced with http and not https.
Merge pull request #6 from jmccann/transprot_chef_install_fix

Fix to work with http chef_omnibus_url