Remove duplication in nav

_includes/nav.html

@@ -1,11 +1,15 @@
-<div class="border-bottom">
+{% if page.url == '/' %}{% assign homepage = true %}{% endif %}
+
+<div class="{% unless homepage %}border-bottom{% endunless %}">
   <div class="container-lg px-3">
     <div class="py-4 d-flex d-flex-row">
       <h1 class="alt-h4 col-4 lh-default v-align-middle">
+        {% unless homepage %}
         <a href="/" class="no-underline text-uppercase text-brand-blue-dark">
           <img class="v-align-middle" style="margin: -20px 8px -8px 0;" src="/assets/probot-head.png" height="36" alt="">
           Probot
         </a>
+        {% endunless %}
       </h1>
       <nav class="text-bold col-8 text-right">
         <a class="text-inherit px-2 d-inline-block" href="/#explore">Explore</a>