Note: After saving, you have to bypass your browser's cache to see the changes. Google Chrome, Firefox, Microsoft Edge and Safari: Hold down the ⇧ Shift key and click the Reload toolbar button. For details and instructions about other browsers, see Wikipedia:Bypass your cache.
$(function(){
	$('#pt-mysandbox a').slice(0,1).attr('href', '/wiki/User:' + mw.config.get('wgUserName') + '/sandbox');
});