fix: handle missing date format fallback (#291)

Author: yashmehrotra

layouts/partials/post.html

@@ -25,7 +25,7 @@ <h1>{{ .Title | markdownify }}</h1>
 
 	{{ if $displayDate }}
           <p class="post-date">{{ dateFormat (or .Site.Params.dateFormat "January 2, 2006") .Date}}
-           {{ if lt .Date .Lastmod }} | Updated {{ dateFormat .Site.Params.dateFormat .Lastmod }}{{ end }}
+           {{ if lt .Date .Lastmod }} | Updated {{ dateFormat (or .Site.Params.dateFormat "January 2, 2006") .Lastmod }}{{ end }}
           </p>
 	{{ end }}