https not http address for twitter

Either should work just fine, as it will redirect automatically on Twitter’s end if that protocol is in use (your link check probably just noticed that redirect). There’s no need to worry about changing it on your site. However, it doesn’t hurt to change it for the future, so it’ll be updated in the next major plugin update, see https://plugins.trac.wordpress.org/changeset/863393/floating-social-media-links.