fix: make sure we don't output empty h1 tags

For #397 we didn't want to have a title, so we ended up rendering an
empty h1 tag, this makes sure that the h1 tag is rendered only if the
title is provided in the front matter.
diff --git a/layouts/_default/section.html b/layouts/_default/section.html
index 7861680..4cab5f2 100644
--- a/layouts/_default/section.html
+++ b/layouts/_default/section.html
@@ -1,8 +1,10 @@
 {{ partial "header.html" . }}
 
-     <article class="static doc {{ .Page.Section }}">
+    <article class="static doc {{ .Page.Section }}">
 
-        <h1>{{ .Title }} </h1>
+        {{ with .Title }}
+            <h1>{{ . }} </h1>
+        {{ end }}
 
         {{ .Content }}
 
diff --git a/layouts/_default/single.html b/layouts/_default/single.html
index 1ddb38a..3065ce7 100644
--- a/layouts/_default/single.html
+++ b/layouts/_default/single.html
@@ -4,7 +4,9 @@
     <main role="main">
         <article class="static doc {{ .Page.Section }}">
 
-          <h1>{{ .Title }}</h1>
+            {{ with .Title }}
+                <h1>{{ . }} </h1>
+            {{ end }}
 
 {{ .Content }}