title: Convert one format into datetime format
body: <p>This is my <code>DataFrame</code>:</p>
  
  <pre><code>issue,received_time
  aa,25-06-15 08:42:43.830000000 PM
  bb,25-06-15 08:42:43.830000000 PM
  </code></pre>
  
  <p>I need output like:</p>
  
  <pre><code>issue,received_time
  aa,25-06-15
  bb,25-06-15
  </code></pre>