fix ref for icon/logo (geopython#2039)

Author: tomkralidis

pygeoapi/templates/_base.html

@@ -26,8 +26,8 @@
     <!--[if lt IE 9]>
       <script src="https://cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv.js"></script>
     <![endif]-->
-    <meta name="twitter:image:src"   content="{% block thumb %}{% endblock %}{% if not self.thumb() %}{{ config['server']['url'] }}/static/img/logo.png{% endif %}" />
-    <meta property="og:image"        content="{{ self.thumb() }}{% if not self.thumb() %}{{ config['server']['url'] }}/static/img/logo.png{% endif %}" />
+    <meta name="twitter:image:src"   content="{% block thumb %}{% endblock %}{% if not self.thumb() %}{{ logo }}{% endif %}" />
+    <meta property="og:image"        content="{{ self.thumb() }}{% if not self.thumb() %}{{ logo }}{% endif %}" />
     <meta name="twitter:site"        content="{{ config['metadata']['identification']['title'] }}" />
     <meta property="og:site_name"    content="{{ config['metadata']['identification']['title'] }}" />    
     <meta name="twitter:card"        content="summary_large_image" />