_includes/sharing-providers/addthis.html

<!-- Addthis BEGIN -->
{%- assign _SHARING_ADDTHIS_ID = site.sharing.addthis.id -%}

{%- if _SHARING_ADDTHIS_ID -%}
  <script type="text/javascript"
    src="//s7.addthis.com/js/300/addthis_widget.js#pubid={{ _SHARING_ADDTHIS_ID }}"></script>
  <div class="addthis_inline_share_toolbox addthis_default_style"></div>
{%- endif -%}
<!-- Addthis END -->