More specific custom property name

hub/templates/hub/tools/postcode.html

@@ -130,7 +130,7 @@ <h2 class="h4">Climate Coalition member?</h2>
         function log_count(numPostcodes) {
             // if trackEvent is defined, log the number of postcodes processed
             if (typeof trackEvent === "function") {
-                    trackEvent("postcode_tool", {"count": numPostcodes});
+                    trackEvent("postcode_tool", {"postcode_count": numPostcodes});
             }
         }