title: convert date to year-month-day using lubridate and pipes
body: <p>I want to turn a date in &quot;day/month/year&quot; to &quot;year/month/day&quot; using lubridate and pipes but I'm having problems. Also, the first row of 'public_release' has day and month switched. The first three rows of both <code>bwg_release</code> and <code>public_release</code> should reflect a January 6 date.
  E.g.</p>
  <pre><code>    datasets %&gt;%
  +   select(bwg_release, public_release)
    bwg_release public_release
  1  06/01/2016     01/06/2018
  2  06/01/2016     06/01/2018
  3  06/01/2016     06/01/2018
  4  17/04/2016     17/04/2016
  </code></pre>
  <p>Current output:</p>
  <pre><code>datasets %&gt;% 
  +   mutate(bwg_release_new_date = format(dmy(bwg_release),&quot;%Y/%m/%d&quot;)) %&gt;%
  +   mutate(public_release_new_date = format(dmy(public_release),&quot;%Y/%m/%d&quot;)) %&gt;%
  +   select(bwg_release_new_date,public_release_new_date)
    bwg_release_new_date public_release_new_date
  1           2016/01/06              2018/06/01
  2           2016/01/06              2018/01/06
  3           2016/01/06              2018/01/06
  4           2016/04/17              2016/04/17     
  </code></pre>
  <p>Desired output:</p>
  <pre><code>bwg_release_new_date public_release_new_date
  1           2016/01/06              2018/01/06
  2           2016/01/06              2018/01/06
  3           2016/01/06              2018/01/06
  4           2016/04/17              2016/04/17
  </code></pre>