title: Obtaining maximun _key value from an Arango Collection
body: <p>Imagine that <code>_key</code> is a series which is always increasing, such as:</p>
  <pre><code>{
    _key:1,
    name: John,
    ...
  },
  {
    _key:2,
    name ...
  },
  ...
  </code></pre>
  <p>I would like to get the maximum value of <code>_key</code> so I can include another element with a <code>_key + 1</code> value.</p>
  <p>I am using <code>python-arango</code> but I could collect the AQL query too.</p>