Fixes an issue with ListFormatter in Internet Explorer

Removes references to the global RegExp object from string.replace() callbacks in ListFormatter.

ListFormatter.format() currently fails in Internet Explorer (9-11; earlier versions not tested), producing output like "last, and last, last, and last" instead of "first, middle, and last".  The code below serves as a test case for the issue:

```
<!DOCTYPE html>
<html>
<head>
	<title>ListFormatter Example</title>
	<script src="lib/assets/javascripts/twitter_cldr/en.js"></script>
</head>
<body>
	<script>
		var formatter = new TwitterCldr.ListFormatter(),
			list = ['ash', 'beech', 'cedar', 'dogwood', 'elm', 'fir', 'gum', 'hickory'];
		
		while (list.length > 0) {
			document.writeln('<p>' + list.length + '. ' + formatter.format(list) + '</p>');
			list.pop();
		}
	</script>
</body>
</html>
```