title: Laravel 4 Query Builder - groupBy Max Date
body: <p>little query question,
  I have table:</p>
  
  <pre><code>id    | user_id | paper_update
  ------------------------------
  1     |    1    | 30-5-2011
  2     |    2    | 30-5-2012
  3     |    3    | 30-5-2012   
  4     |    1    | 30-5-2013  
  5     |    2    | 30-5-2013  
  6     |    3    | 30-5-2014  
  7     |    4    | 30-5-2014  
  8     |    5    | 30-5-2014
  9     |    5    | 30-5-2015 
  10    |    5    | 30-5-2016
  11    |    1    | 30-5-2010
  -------------------------------
  </code></pre>
  
  <p>What I'm looking to do is to select only the records where <code>paper_update</code> is max between records with the same <code>user_id</code>, actually I want to group by the <code>user_id</code> in order to the max <code>paper_update</code>.
  so for this table it will return  this:</p>
  
  <pre><code>id    | user_id | paper_update
  ------------------------------
  4     |    1    | 30-5-2013  
  5     |    2    | 30-5-2013  
  6     |    3    | 30-5-2014  
  7     |    4    | 30-5-2014  
  10    |    5    | 30-5-2016 
  -------------------------------
  </code></pre>