title: How to fix 'could not find compatible version for gem "rails"'?
body: <p>Im literaly bumping my head into a wall and I can not find a solution by myself about this problem.</p>
  
  <p>I'm starting a project with Solidus , a Spree commerce fork. I played around with the gem for a litle while and now that I am ready to get serious and start to develop , I create a new project ad I'm bumping into this nasty error : </p>
  
  <pre><code>Bundler could not find compatible versions for gem "rails":
    In snapshot (Gemfile.lock):
      rails (= 5.1.2)
  
    In Gemfile:
      rails (~&gt; 5.1.2)
  
      solidus was resolved to 1.0.0, which depends on
        solidus_core (= 1.0.0) was resolved to 1.0.0, which depends on
          rails (~&gt; 4.2.0)
  
  Running `bundle update` will rebuild your snapshot from scratch, using only
  the gems in your Gemfile, which may resolve the conflict.
  </code></pre>
  
  <p>and <code>bundle update</code> is not solving my problem... I am running out of solution and will appreciate some hands in help in how to fix this problem.</p>
  
  <p>Thanks</p>