title: Why I am getting Could not find multi_json-1.3.1 in any of the sources?
body: <p>I have a simple Rails application I want to deploy to Heroku. When I run the below command</p>
  
  <pre><code>git push heroku master
  </code></pre>
  
  <p>The below error message is displayed.</p>
  
  <pre><code> Could not find multi_json-1.3.1 in any of the sources
   !
   ! Failed to install gems via Bundler.
   !
   ! Heroku push rejected, failed to compile Ruby/rails app
  </code></pre>
  
  <p>Here is my Gemfile</p>
  
  <pre><code> gem 'rails', '3.2.3'
   gem 'pg'
   group :assets do
    gem 'sass-rails',   '~&gt; 3.2.3'
    gem 'coffee-rails', '~&gt; 3.2.1'
    gem 'therubyracer', :platform =&gt; :ruby
    gem 'uglifier', '&gt;= 1.0.3'
  end
  gem 'jquery-rails'
  </code></pre>