Fix typo in the header URL

The hugo docs (https://gohugo.io/content-management/organization/) specify that the default location for a user's posts is in the `posts/` directory. This change fixes the archive link for users who stick to the default.

layouts/partials/nav.html

@@ -3,7 +3,7 @@
 	{{ if not .IsHome }}
 		<a href='{{ .Site.BaseURL }}'> <span class="arrow">←</span>{{ with .Site.Params.home }}{{ . }}{{ else }}Home{{ end }}</a>
 	{{ end }}
-	<a href='{{ .Site.BaseURL }}post'>{{ with .Site.Params.archive }}{{ . }}{{ else }}Archive{{ end }}</a>
+	<a href='{{ .Site.BaseURL }}posts'>{{ with .Site.Params.archive }}{{ . }}{{ else }}Archive{{ end }}</a>
 	<a href='{{ .Site.BaseURL }}tags'>{{ with .Site.Params.tags }}{{ . }}{{ else }}Tags{{ end }}</a>
 	<a href='{{ .Site.BaseURL }}about'>{{ with .Site.Params.about }}{{ . }}{{ else }}About{{ end }}</a>