_includes/twitter.html
<a href="https://twitter.com/share" class="twitter-share-button"
data-via="{{ site.author.twitter }}" data-lang="en" data-size="large">Tweet</a>
<script>
!function(d,s,id){
var js,fjs=d.getElementsByTagName(s)[0];
if(!d.getElementById(id)){
js=d.createElement(s);
js.id=id;
js.src="//platform.twitter.com/widgets.js";
fjs.parentNode.insertBefore(js,fjs);
}
}(document,"script","twitter-wjs");
</script>