Update relative url for logo

Author: lucyb

_includes/header.html

@@ -4,8 +4,8 @@
     {%- assign default_paths = site.pages | map: "path" -%}
     {%- assign page_paths = site.header_pages | default: default_paths -%}
     {%- assign titles_size = site.pages | map: 'title' | join: '' | size -%}
-    <a class="site-title" rel="author" href="{{ "/" | relative_url }}">
-      <img src="{{ "/" | relative_url }}/assets/images/pythonnw_logo.png"
+    <a class="site-title" rel="author" href="{{ '/' | relative_url }}">
+      <img src="{{ '/assets/images/pythonnw_logo.png' | relative_url }}"
       width="50px" height="50px" />
       {{ site.title | escape }}
     </a>