title: Is there any difference between the `:key => "value"` and `key: "value"` hash notations?
body: <p>Is there any difference between <code>:key =&gt; "value"</code> (hashrocket) and <code>key: "value"</code> (Ruby 1.9) notations?</p>
  
  <p>If not, then I would like to use <code>key: "value"</code> notation. Is there a gem that helps me to convert from <code>:x =&gt;</code> to <code>x:</code> notations?</p>