upgrade sprockets

bundle_update_result.txt

$ bundle update
Fetching gem metadata from https://rubygems.org/..
Bundler could not find compatible versions for gem "sprockets":
  In Gemfile:
    sprockets (~> 2.2.0) ruby

    rails (= 3.2.8) ruby depends on
      sprockets (2.1.3)

Gemfile.diff

 source 'https://rubygems.org'
 
 ruby '1.9.3'
-gem 'rails', '3.2.8'
+gem 'rails', git: "git://github.com/rails/rails.git", branch: "3-2-stable"
 gem 'thin'
 
 gem 'pg'

 ...