Is there a better option than what I did to fix this, so I don't have to remember to do this manually whenever the plugin is updated?
I had to edit 2 lines in the code to make this work with https without getting the mixed content warning and no pinning:
e.setAttribute('src','https://assets.pinterest.com/js/pinmarklet.js?r=' + Math.random()*99999999);
$link_href = 'https://pinterest.com/pin/create/button/?url=' . rawurlencode( $post_url ) . '&media=' . rawurlencode( $image_url ) . '&description='. rawurlencode( $description );