Valid Chef version strings fail validation under RubyGems 2.0+

[schisamo]

This was uncovered when Travis-CI ran the unit test:
https://travis-ci.org/schisamo/vagrant-omnibus/builds/6449078

The current version of Vagrant (1.2.1) ships a pre-2.0 version of RubyGems so this shouldn't be a huge deal for end-users:

% /Applications/Vagrant/embedded/bin/gem --version
1.8.23

[tknerr]

FYI: I was also running into the SSL cert verification issue described here:
http://railsapps.github.io/openssl-certificate-verify-failed.html

As a result, I got:

There are errors in the configuration of this machine. Please fix
the following errors and try again:

vagrant-omnibus:
* '11.10.4' is not a valid version of Chef.

A list of valid versions can be found at: http://www.opscode.com/chef/install/

Baiscally any Chef version specified via config.omnibus.chef_version failed.

This was on Windows 7 box, with ruby 1.9.3p125 and rubygems 2.0.3

I could fix it by downloading the cacert.pem and setting SSL_CERT_FILE as described here:
https://gist.github.com/fnichol/867550

After that it worked again...