Use the actual next post in posts_collate

_includes/JB/posts_collate

@@ -23,8 +23,8 @@ Usage:
   {% for post in posts_collate  %}
     {% capture this_year %}{{ post.date | date: "%Y" }}{% endcapture %}
     {% capture this_month %}{{ post.date | date: "%B" }}{% endcapture %}
-    {% capture next_year %}{{ post.previous.date | date: "%Y" }}{% endcapture %}
-    {% capture next_month %}{{ post.previous.date | date: "%B" }}{% endcapture %}
+    {% capture next_year %}{{ posts_collate[forloop.index].date | date: "%Y" }}{% endcapture %}
+    {% capture next_month %}{{ posts_collate[forloop.index].date | date: "%B" }}{% endcapture %}
 
     {% if forloop.first %}
       <h2>{{this_year}}</h2>
@@ -52,4 +52,4 @@ Usage:
     {% endif %}
   {% endfor %}
 {% endif %}
-{% assign posts_collate = nil %}
+{% assign posts_collate = nil %}