Corrected installation instructions

You can't install 2.0.0.pre.1 from rubygems.org, so specified git path instead.
Used GitHub-specific source

Since this:
  github: "resque/resque"

looks cleaner than this:
  :git => "git@github.com:resque/resque.git"
Merge pull request #1073 from evjan/master

Corrected installation instructions