fix GH-332

Signed-off-by: Junjie Yuan <junjieraw@gmail.com>

layouts/partials/site-navigation.html

@@ -2,7 +2,7 @@
   <div class="flex-l justify-between items-center center">
     <a href="{{ .Site.Home.RelPermalink }}" class="f3 fw2 hover-white no-underline white-90 dib">
       {{ with .Site.Params.site_logo }}
-        <img src="{{ . }}" class="w100 mw5-ns" alt="{{ $.Site.Title }}" />
+        <img src="{{ relURL ($.Site.Params.site_logo) }}" class="w100 mw5-ns" alt="{{ $.Site.Title }}" />
       {{ else }}
         {{ .Site.Title }}
       {{ end }}