title: How to convert Date into UTC in MongoMapper & Ruby/Rails?
body: <p>I added this line of code </p>
  
  <pre><code>self.auth_history.push [start_date, self.coupon_code]
  </code></pre>
  
  <p>And got this error message </p>
  
  <pre><code>Date is not currently supported; use a UTC Time instance instead.
  </code></pre>
  
  <p>I also tried <code>start_date.utc</code>, but it didn't work either.</p>
  
  <p>Please help.  Thanks.</p>