title: Refresh data retrieved by a custom function in Google Sheet
body: <p>I've written a custom Google Apps Script that will receive an <code>id</code> and fetch information from a web service (a price).</p>
  
  <p>I use this script in a spreadsheet, and it works just fine. My problem is that these prices change, and my spreadsheet doesn't get updated.</p>
  
  <p>How can I force it to re-run the script and update the cells (without manually going over each cell)?</p>