Error when attempting to install attachment_fu using bundler

[vmcilwain]

Hello all,

I am trying to install attachment_fu on a rails 3 app using bundler and I am getting the following error:

Could not find gem 'attachment_fu (>= 0) ruby' in git://github.com/technoweenie/attachment_fu.git (at master).
Source does not contain any versions of 'attachment_fu (>= 0) ruby'

My gem file has the following line in it:

gem 'attachment_fu', :git => "git://github.com/technoweenie/attachment_fu.git", :branch => 'master'

Can anyone tell me what I need to change to get attachment_fu to install properly?