title: Convert Pandas date column from dd-mmm-yy to yyyy-mm-dd
body: <p>I have a Pandas Dataframe that stores date in the format <code>19-Jul-18</code>. I am trying to convert it to <code>2018-07-19</code></p>
  
  <p>I tried doing <code>pd.to_datetime(df['date'])</code> but it dint help.</p>