add missing caption so that image shows

Author: polyfractal

300_Aggregations/35_date_histogram.asciidoc

@@ -278,7 +278,7 @@ when it comes to charting aggregations.  For example, here is a dashboard in
 Kibana built with a variety of aggregations:
 
 [[kibana-img]]
-image::images/300_35_kibana.png
+image::images/300_35_kibana.png["Kibana - a real time analytics dashboard built with aggregations"]
 
 Due to the real-time nature of aggregations, dashboards like this are easy to query,
 manipulate and interact with.  This makes them ideal for non-technical employees