Put title on series page in div.page-title like other taxonomy pages

This must've gotten out of sync somehow throughout the history. It
slightly changes the margins by disabling the default one on h1, which
is slightly larger than the breadcrumb nav margin-block's.

layouts/series/taxonomy.html

@@ -1,8 +1,10 @@
 {{ define "main" }}
-    <h1>
-        {{ partial "icon.html" "files" }}
-        {{ .Title | markdownify }}
-    </h1>
+    <div class="page-title">
+        <h1>
+            {{ partial "icon.html" "files" }}
+            {{ .Title | markdownify }}
+        </h1>
+    </div>
 
     {{ with .Content }}
         {{ . }}