Fix credits attribute in further shortcode

Closes #30 (closed)

templates/shortcodes/further.html

@@ -14,8 +14,8 @@
               <figure class="image is-4by3">
                 {% set image = resize_image(path="@/" ~ page.colocated_path ~ "/" ~ further.image, width=800, height=600) -%}
                 <img src="{{image.url}}" alt="{{further.alt}}" />
-                {% if further.image.credits %}
-                  <figcaption class="p-1 has-text-white has-background-black is-size-7 is-italic">{{ further.image.credits }}</figcaption>
+                {% if further.credits %}
+                  <figcaption class="p-1 has-text-white has-background-black is-size-7 is-italic">{{ further.credits }}</figcaption>
                 {% endif %}
               </figure>
             </a>