Change RSS lastBuildDate to use section dates

layouts/_default/rss.xml

@@ -3,7 +3,7 @@
 {{ $copyright := site.Copyright }}
 {{ $description := or $page.Description "Recent content" }}
 {{ $html := $page.AlternativeOutputFormats.Get "html" }}
-{{ $lastbuilddate := and $page.PublishDate (not $page.PublishDate.IsZero) ($page.PublishDate.Format "Mon, 02 Jan 2006 15:04:05 -0700") }}
+{{ $lastbuilddate := (partial "paige/changed.html" $page).Format "Mon, 02 Jan 2006 15:04:05 -0700" }}
 {{ $language := site.LanguageCode | default site.Language.Lang }}
 {{ $limit := site.Config.Services.RSS.Limit }}
 {{ $link := $page.Permalink }}

layouts/partials/paige/changed.html

@@ -0,0 +1,8 @@
+{{ $page := . }}
+{{ $max := "" }}
+{{ range $page.RegularPages }}
+    {{ if or (not $max) (lt $max .PublishDate) }}
+        {{ $max = .PublishDate }}
+    {{ end }}
+{{ end }}
+{{ return $max }}