title: time relative formats : get the date of the first Sunday of last year
body: <p>I want to retrieve the date of the first Sunday of last year,
  but i have a problem</p>
  <pre><code>$date = new DateTime('first sunday of august last year');
  </code></pre>
  <p>gives me as a result :</p>
  <pre><code>DateTime Object ( [date] =&gt; 2020-08-01 00:00:00.000000 [timezone_type] =&gt; 3 [timezone] =&gt; Europe/Berlin ) 
  // saturday
  </code></pre>
  <p>but I want :</p>
  <pre><code>DateTime Object ( [date] =&gt; 2020-08-02 00:00:00.000000 [timezone_type] =&gt; 3 [timezone] =&gt; Europe/Berlin ) 
  // sunday
  </code></pre>
  <p>is this a bug or am I at fault ?</p>