IE8 support

[oblador]

Throws a lot of errors on IE8 including Error: 'undefined' is null or not an object after each letter you type in the card number field. Would be nice to support it.

[dmix]

Confirmed to not work on IE8. One example is this line:

  $target = angular.element(e.currentTarget);

Whereas IE8 requires using:

  var el = (event.currentTarget) ? event.currentTarget : event.srcElement;
  $target = angular.element(el);

Any plans to support IE8? I might dig into it more depending on my requirements for a project I'm working on.