Change name DateForm to DateFormat, complete git-footer.html upgrade

layouts/posts/list.html

@@ -6,7 +6,7 @@
       <a href="{{ .RelPermalink }}">{{ .Title }}</a>
     </h2>
     <h5>
-      <strong>{{ .Date.Format .Site.Params.DateForm }}</strong>
+      <strong>{{ .Date.Format .Site.Params.DateFormat }}</strong>
     </h5>
     <p class="markdown">
       {{- .Summary -}}

layouts/posts/single.html

@@ -2,7 +2,7 @@
 <header>
   <h1>{{ .Title }}</h1>
   <h5>
-    <strong>{{ .Date.Format .Site.Params.DateForm  }}</strong>
+    <strong>{{ .Date.Format .Site.Params.DateFormat  }}</strong>
   </h5>
 </header>
 <article class="markdown">