title: Rails 5.1.0.beta1 "bundle update rails" has gem conflict
body: <p>I just cant upgrade rails beta version. 
  My current rails version is 5.0.2 and would like to upgrade to 5.1.0.beta1 version.</p>
  
  <p>ruby -v 
  <code>
  ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]</code></p>
  
  <p>bundle update rails</p>
  
  <pre><code>Fetching gem metadata from http://rubygems.org/........
  Fetching version metadata from http://rubygems.org/..`
  Fetching dependency metadata from http://rubygems.org/.
  Resolving dependencies...
  Bundler could not find compatible versions for gem "railties":
    In Gemfile:
      coffee-rails (~&gt; 4.1.0) was resolved to 4.1.1, which depends on
        railties (&lt; 5.1.x, &gt;= 4.0.0)
  
      rails (~&gt; 5.1.0.beta1) was resolved to 5.1.0.beta1, which depends on
        railties (= 5.1.0.beta1)
  
      sass-rails (~&gt; 5.0) was resolved to 5.0.6, which depends on
        railties (&lt; 6, &gt;= 4.0.0)
  </code></pre>
  
  <p>bundle update</p>
  
  <pre><code>Fetching https://github.com/megetron/active_merchant_tranzila.git
  Fetching https://github.com/megetron/active_shipping.git
  Fetching gem metadata from http://rubygems.org/........
  Fetching version metadata from http://rubygems.org/..
  Fetching dependency metadata from http://rubygems.org/.
  Resolving dependencies...
  Bundler could not find compatible versions for gem "railties":
    In Gemfile:
      coffee-rails (~&gt; 4.1.0) was resolved to 4.1.0, which depends on
        railties (&lt; 5.0, &gt;= 4.0.0)
  
      devise was resolved to 4.2.0, which depends on
        railties (&lt; 5.1, &gt;= 4.1.0)
  
      rails (~&gt; 5.1.0.beta1) was resolved to 5.1.0.beta1, which depends on
        railties (= 5.1.0.beta1)
  
      sass-rails (~&gt; 5.0) was resolved to 5.0.6, which depends on
        railties (&lt; 6, &gt;= 4.0.0)
  
      web-console (~&gt; 2.0) was resolved to 2.3.0, which depends on
        railties (&gt;= 4.0)
  </code></pre>