title: Using n() with summarise_all
body: <p>Works fine:</p>
  
  <pre><code>stats = c('mean', 'median', 'sd', 'max', 'min')
  sumtable = iris %&gt;% select(-Species) %&gt;%  summarise_all(.funs = stats)
  </code></pre>
  
  <p>Doesn't work:</p>
  
  <pre><code>stats = c('mean', 'median', 'sd', 'max', 'min', 'n')
  sumtable = iris %&gt;% select(-Species) %&gt;% summarise_all(.funs = stats)
  Error in summarise_impl(.data, dots) : `n()` does not take arguments
  </code></pre>
  
  <p>Please advise.</p>