title: How to update all records in a collection using graphql
body: <p>I'm using Graph.cool graphql as a service and am wondering how to do a mass update to the collection, similar to a SQL update.</p>
  
  <p>In my case I need to update the suffix of a url, in the imageUrl column of my database.  I need to swap out a {someid}_sm.jpg to {someid}_lg.jpg</p>
  
  <p>How do I do that with a graphql mutation?  I don't want to reload the entire dataset again and am looking for a way to do it that doesn't involve manually interating through the entire list with a graphql client.</p>
  
  <pre><code>mutation {
    updatePost() // what goes here?
  }
  </code></pre>