Update to Hugo 0.53 and remove all .Site references (#12079)

* Remove all .Site variable references

* Update Hugo version in Travis CI config and Makefile

layouts/partials/tree.html

@@ -2,7 +2,7 @@
 {{ template "section-tree-nav" (dict "ctx" . "section" .) }}
 {{ define "section-tree-nav" }}
 	{{ $pages :=  (union .section.Pages .section.Sections) }}
-	{{ with $.ctx.Site.Params.language_alternatives }}
+	{{ with site.Params.language_alternatives }}
 		{{ range . }}	
 			{{ with (where $.section.Translations ".Lang" . ) }}
 			{{ $p := index . 0 }}
@@ -34,4 +34,4 @@
 {{ define "section-tree-nav-page" }}
 {{ $isForeignLanguage := (ne .page.Lang $.ctx.Lang)}}
 <a class="item" {{ if $isForeignLanguage }}target="_blank" {{ end }}data-title="{{ .page.LinkTitle }}{{ if $isForeignLanguage }} <small>({{ .page.Lang | upper }})</small>{{ end }}" href="{{ .page.RelPermalink }}"></a>
-{{ end }}
+{{ end }}