Eliminating the need to have jQuery for this plugin to work

Just a simple switch of the usage of `element.width()` for `element.prop('offsetWidth')` so that jQuery is not required.

Some users of Angular prefer not to load jQuery and want to use the default jQlite that comes with Angular - this will accommodate both sets of users by using .prop() in place of the unsupported-by-jqlite width(). All tests still pass.

Thanks!