title: Phoenix 1.0 to 1.2: Unchecked dependencies for environment dev
body: <p>I am updating Phoenix from 1.0 to 1.2
  I followed the steps to upgrade from 1.0 to 1.1 and then 1.1.x to 1.2.0</p>
  
  <p>Whenever I try to compile I am getting the following error:</p>
  
  <pre><code>Unchecked dependencies for environment dev:
  * phoenix_pubsub_redis (Hex package)
    the dependency does not match the requirement "~&gt; 2.1", got "1.0.0"
  * phoenix_html (Hex package)
    the dependency does not match the requirement "~&gt; 2.6", got "2.2.0"
  * phoenix (Hex package)
    the dependency does not match the requirement "~&gt; 1.2.0", got "1.0.3"
  * phoenix_ecto (Hex package)
    the dependency does not match the requirement "~&gt; 3.0-rc", got "1.2.0"
  ** (Mix) Can't continue due to errors on dependencies
  </code></pre>
  
  <p>Does anyone know what is going on or how this could be fixed?</p>