Fix for issue #11811https://github.com/woothemes/woocommerce/issues/11811
IE handles hitting <ENTER> on an input field differently than
Chrome or Firefox in that it finds the nearest submit button
and fires the event from it instead of the actual text field
from which the user hit <ENTER>.
This commit catches the <ENTER> key event before the submit happens
and forces the cart_submit handling on that event instead.
81d186000d