Use Hugo's partial-returning where possible

Signed-off-by: Danila Fedorin <danila.fedorin@gmail.com>

layouts/_partials/uniquebyseries.html

@@ -1,14 +1,14 @@
-{{- $scratch := .scratch -}}
-{{- $scratch.Set "pages" slice -}}
+{{- $pages := slice -}}
 {{- $tmpScratch := newScratch -}}
 {{- range $post := (where (where site.Pages.ByDate.Reverse "Section" "blog") ".Kind" "!=" "section") -}}
 {{- $term := index ($post.GetTerms "series") 0 -}}
 {{- if (and $term (not ($term.Param "donotunique"))) -}}
 {{- if not ($tmpScratch.Get $term.Permalink) -}}
 {{- $tmpScratch.Set $term.Permalink true -}}
-{{- $scratch.Add "pages" $post -}}
+{{- $pages = $pages | append $post -}}
 {{- end -}}
 {{- else -}}
-{{- $scratch.Add "pages" $post -}}
+{{- $pages = $pages | append $post -}}
 {{- end -}}
 {{- end -}}
+{{- return $pages -}}