Add attributes to base_url link in atom template (#2261)

The `rel` and `type` HTML attributes are needed in the `base_url` (or
`section.permalink`) link so feed aggregators know that's the HTML page
that corresponds to the atom feed.

Note: The RSS template doesn't have this issue.

components/templates/src/builtins/atom.xml

@@ -8,8 +8,8 @@
     {%- if config.description %}
     <subtitle>{{ config.description }}</subtitle>
     {%- endif %}
-    <link href="{{ feed_url | safe }}" rel="self" type="application/atom+xml"/>
-    <link href="
+    <link rel="self" type="application/atom+xml" href="{{ feed_url | safe }}"/>
+    <link rel="alternate" type="text/html" href="
       {%- if section -%}
         {{ section.permalink | escape_xml | safe }}
       {%- else -%}
@@ -41,7 +41,7 @@
           </name>
         </author>
         {% endfor %}
-        <link rel="alternate" href="{{ page.permalink | safe }}" type="text/html"/>
+        <link rel="alternate" type="text/html" href="{{ page.permalink | safe }}"/>
         <id>{{ page.permalink | safe }}</id>
         {% if page.summary %}
         <summary type="html">{{ page.summary }}</summary>