Instead of changing around the whole header php for such a minor change, try this simple and clean (but still hacky) fix. Simply add the following lines to your custom.css:
ul.wc-nav li.cart a > span { padding-left: 20px; }
ul.wc-nav li.cart a > span:after { content: 'items'; }
ul.wc-nav li.cart a > span span.amount { position: relative; left: -20px; }
This also adds 'items' after the number.