Fix buggy match for top of documentation

The match was against the page title, which isn't as stable as the
filename of the page. Switch to matching by filename.

Author: Tim Bannister

layouts/partials/sidebar-tree.html

@@ -26,13 +26,13 @@
 {{ $show := or (eq $s $p.FirstSection) (and (not $p.Site.Params.ui.sidebar_menu_compact) ($p.IsDescendant $s)) }}
 {{ $sid := $s.RelPermalink | anchorize }}
 <ul class="td-sidebar-nav__section pr-md-3">
+  {{ if (ne $s.File.Path "docs/_index.md") }}
   <li class="td-sidebar-nav__section-title">
     <a  href="{{ $s.RelPermalink }}" class="align-left pl-0 pr-2{{ if not $show }} collapsed{{ end }}{{ if $active}} active{{ end }} td-sidebar-link td-sidebar-link__section">
-      {{ if not (eq $s.LinkTitle "Documentation") }}
       {{ $s.LinkTitle }}
-      {{ end }}
     </a>
   </li>
+  {{ end }}
   <ul>
     <li class="collapse {{ if $show }}show{{ end }}" id="{{ $sid }}">
       {{ $pages := where (union $s.Pages $s.Sections).ByWeight ".Params.toc_hide" "!=" true }}