title: How to add a year to a column of dates in pandas
body: <p>I am attempting to add a year to a column of dates in a pandas dataframe, but when I use <code>pd.to_timedelta</code> I get additional hours &amp; minutes. I know I could take the updated time and truncate the hours, but I feel like there must be a way to add a year precisely. My attempt as follows:</p>
  
  <pre><code>import pandas as pd
  dates = pd.DataFrame({'date':['20170101','20170102','20170103']})
  dates['date'] = pd.to_datetime(dates['date'], format='%Y%m%d')
  dates['date2'] = dates['date'] +  pd.to_timedelta(1, unit='y')
  dates
  </code></pre>
  
  <p>yields:</p>
  
  <pre><code>Out[1]: 
      date        date2
  0   2017-01-01  2018-01-01 05:49:12
  1   2017-01-02  2018-01-02 05:49:12
  2   2017-01-03  2018-01-03 05:49:12
  </code></pre>
  
  <p>How can I add a year without adding 05:49:12 HH:mm:ss?</p>