support ruby 2.0

@zendesk/samson @grosser 

#59
Just merge and I'll try to clean it up

On Wed, Oct 8, 2014 at 2:14 PM, Steven Davidovitz <notifications@github.com>
wrote:

> In app/models/job_execution.rb:
>
> > @@ -165,11 +165,10 @@ def setup!(dir)
> >
> >    def commit_from_ref(repo_dir, ref)
> >      description = Dir.chdir(repo_dir) do
> > -      Tempfile.create("ref-description") do |file|
> > -        system("git", "describe", "--long", "--tags", "--all", ref, out: file.fileno)
> > -        file.rewind
> > -        file.read.strip
> > -      end
> > +      file = Tempfile.new("ref-description")
>
> I just copied the old behavior, I have no idea. Can you do that?
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/zendesk/samson/pull/138/files#r18612834>.
>