[PATCH] tpl/tplimpl: Update RSS template

- Use publication date for pubdate
- Include version in generator element

cherry-picked from gohugoio/hugo@f0a26cf

Author: jmooring

layouts/_default/rss.xml

@@ -55,7 +55,7 @@
       <link>{{ index . 0 | absURL }}</link>
     </image>
     {{- end }}
-    <generator>Hugo -- gohugo.io</generator>
+    <generator>Hugo -- {{ hugo.Version }}</generator>
     <language>{{ site.Language.LanguageCode }}</language>{{ with $authorEmail }}
     <managingEditor>{{.}}{{ with $authorName }} ({{ . }}){{ end }}</managingEditor>{{ end }}{{ with $authorEmail }}
     <webMaster>{{ . }}{{ with $authorName }} ({{ . }}){{ end }}</webMaster>{{ end }}{{ with site.Copyright }}
@@ -69,7 +69,7 @@
     <item>
       <title>{{ .Title }}</title>
       <link>{{ .Permalink }}</link>
-      <pubDate>{{ .Date.Format "Mon, 02 Jan 2006 15:04:05 -0700" | safeHTML }}</pubDate>
+      <pubDate>{{ .PublishDate.Format "Mon, 02 Jan 2006 15:04:05 -0700" | safeHTML }}</pubDate>
       {{- with $authorEmail }}<author>{{ . }}{{ with $authorName }} ({{ . }}){{ end }}</author>{{ end }}
       <guid>{{ .Permalink }}</guid>
       <description>{{ with .Description | html }}{{ . }}{{ else }}{{ .Summary | html }}{{ end -}}</description>