想要试试 rails action cable，但是 rails 5 死活装不上。不报错，bundle install 一直停在

Fetching https://github.com/rails/rails.git

以下是 Gemfile.

source 'https://rubygems.org'

ruby '2.3.0'
gem 'rails', git: "https://github.com/rails/rails.git", tag: 'v5.0.0.beta1'

gem 'sqlite3'
gem 'sass-rails'
gem 'uglifier'
gem 'coffee-rails'

gem 'jquery-rails'
gem 'turbolinks'
gem 'jbuilder', '~> 2.0'
# gem 'sdoc', '~> 0.4.0',          group: :doc

gem 'spring',        group: :development

gem 'puma'

求有经验的同学指点。