fix: remove trailing slashes

Guess what, on https://gohugo.io/functions/relurl/ it says

> As a best practice, never include a leading slash when using this function.

Fixes https://github.com/janraasch/hugo-bearblog/issues/65

layouts/_default/list.html

@@ -3,7 +3,7 @@
   {{ if .Data.Singular }}
   <h3 style="margin-bottom:0">Filtering for "{{ .Title }}"</h3>
   <small>
-    <a href="{{ "/blog" | relURL }}">Remove filter</a>
+    <a href="{{ "blog" | relURL }}">Remove filter</a>
   </small>
   {{ end }}
   <ul class="blog-posts">

layouts/partials/header.html

@@ -1,4 +1,4 @@
-<a href="{{ "/" | relURL }}" class="title">
+<a href="{{ "" | relURL }}" class="title">
   <h2>{{ .Site.Title }}</h2>
 </a>
 <nav>{{- partial "nav.html" . -}}</nav>

layouts/partials/nav.html

@@ -1,7 +1,7 @@
-<a href="{{ "/" | relURL }}">Home</a>
+<a href="{{ "" | relURL }}">Home</a>
 {{ range .Site.Menus.main }}
 <a href="{{ .URL }}">{{ .Name }}</a>
 {{ end }}
 {{ with .Site.GetPage "/blog" }}
-<a href="{{ "/blog" | relURL }}">Blog</a>
+<a href="{{ "blog" | relURL }}">Blog</a>
 {{ end }}