title: Add Pod dependency with source to .podspec
body: <p>I am trying to add the following dependency to my Podspec</p>
  
  <pre><code>s.dependency 'Apollo/WebSocket', :git =&gt; 'https://github.com/apollographql/apollo-ios'
  </code></pre>
  
  <hr>
  
  <p>Here's what I get in my Terminal whenever I try to run <code>pod lib lint MyPodName.podspec</code>:</p>
  
  <pre><code>- ERROR | spec: The specification defined in `MyPodName.podspec` could not be loaded.
  
  
  [!] Invalid `MyPodName.podspec` file: [!] Unsupported version requirements.
  
   #  from &lt;PathToMyPodspec&gt;/MyPodName.podspec:36
   #  -------------------------------------------
   #    
   &gt;    s.dependency 'Apollo/WebSocket', :git =&gt; 'https://github.com/apollographql/apollo-ios'
   #    
   #  -------------------------------------------
  </code></pre>
  
  <hr>
  
  <p>I have successfully used it as a Pod in one of my iOS projects. But now that I am creating a pod myself, I am struggling to understand what I should do to make it work.</p>
  
  <p>Thank you in advance!</p>