[ticket/13876] set webfont async to true

PHPBB3-13876

phpBB/styles/prosilver/template/overall_header.html

@@ -38,6 +38,7 @@
 	(function(d) {
 		var wf = d.createElement('script'), s = d.scripts[0];
 		wf.src = 'https://ajax.googleapis.com/ajax/libs/webfont/1.5.18/webfont.js';
+		wf.async = true;
 		s.parentNode.insertBefore(wf, s);
 	})(document);
 </script>