Allow prereleases to be included in the chefdk

@lamont-granquist @danielsdeleo I don't see any way to do it.  And  https://github.com/rubygems/rubygems/blob/master/lib/rubygems/version.rb#L282 does not give one hope ... but I'll modify the comments for ELI5 before I check in, unless there is something else :)