Use 'evt.shiftKey' instead of matching 'charCodes'

The shortcut wasn't running consistently and was blocking
<kbd>Cmd+L</kbd> on Chrome 38. Instead of going to the location bar
it would tooggle the list. Strangely, it did not override
<kbd>Cmd+N</kbd>. Using `evt.shiftKey` instead of matching the `charCode`
to the uppercase letter solves the problem.