separating-jekyll-blog-categories-by-comma

<div class="categories">
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  {% for category in page.categories %}
    {% if forloop.last %}
      <a href="{{site.url}}/categories/{{category}}">{{category}}</a>
    {% else %}
      <a href="{{site.url}}/categories/{{category}}">{{category}}</a>,
    {% endif %}
  {% endfor %}
</div>