Update generator README for correct Ruby version
Update generator README for correct Ruby version

As Omnibus now requires Ruby 2.0.0+, the generated README.md should be updated.
jamesn/omnibus,strangelittlemonkey/omnibus,DataDog/omnibus-ruby,chef/omnibus,higanworks/omnibus,chef/omnibus,jamesn/omnibus,strangelittlemonkey/omnibus,higanworks/omnibus,DataDog/omnibus-ruby,Scalr/omnibus,Altiscale/omnibus,Scalr/omnibus,rapid7/omnibus,rapid7/omnibus,higanworks/omnibus,Altiscale/omnibus,szechyjs/omnibus,Altiscale/omnibus,Scalr/omnibus,strangelittlemonkey/omnibus,szechyjs/omnibus,chef/omnibus,jamesn/omnibus,DataDog/omnibus-ruby,rapid7/omnibus,szechyjs/omnibus