title: How to coerce string to datetime in Python Cerberus?
body: <p>I'm trying to coerce string as date so it can validate date data type, but it still returns <code>False</code>:</p>
  <pre><code>from cerberus import Validator
  from datetime import datetime
  
  v = Validator()
  v.schema = {'start_date': {'type': 'date','coerce':datetime.date}}
  v.validate({'start_date': '2017-10-01'})
  &gt;&gt;&gt; False
  </code></pre>
  <p>I have tried to use the integer and it works. I'm not sure why date conversion is not working:</p>
  <pre><code>v = Validator()
  v.schema = {'amount': {'type': 'integer','coerce': int}}
  v.validate({'amount': '2'})
  &gt;&gt;&gt; True
  </code></pre>
  <p>Any help would be appreciated.</p>