使用Rail 3从github安装gem

Question

我需要从github安装wicked_pdf gem。我还更新了Gemfile但是当我运行bundle install时，它给了我以下信息。

You need to install git to be able to use gems from git repositories. For help
installing git, please refer to GitHub's tutorial at
https://help.github.com/articles/set-up-git

我有下面给出的Gemfile。

  

的Gemfile：

source 'https://rubygems.org'

gem 'rails', '3.2.19'
gem 'mysql'
group :assets do
  gem 'sass-rails',   '~> 3.2.3'
  gem 'coffee-rails', '~> 3.2.1'

  gem 'uglifier', '>= 1.0.3'
end

gem 'jquery-rails'
gem "bcrypt-ruby", :require => "bcrypt"
gem 'momentjs-rails', '>= 2.8.1'
gem 'bootstrap3-datetimepicker-rails', '~> 4.0.0'
gem 'bootstrap-datepicker-rails', '>= 0.6.21'
gem 'will_paginate', '~> 3.0'
gem 'wicked_pdf', :github => 'mileszs/wicked_pdf', :branch => 'master'

我已经在我的系统上安装了git-cell，我使用的是win-7 64位。请帮我解决这个问题。