Support mmark (replace <hr> by <hr />)

Mmark produces "<hr>" while blackfriday produces "<hr />". A simple
replace allows to support both.

layouts/partials/reveal-hugo/slides.html

@@ -4,6 +4,8 @@
   {{- if ne (len .Content) 0 -}}
     <!-- Remove the <hr /> tag generated by blackfriday for footnotes -->
     {{- $content := replace .Content "<div class=\"footnotes\">\n\n<hr />" "<div class=\"footnotes\">" -}}
+    <!-- Support both <hr /> (blackfriday) and <hr> (mmark) -->
+    {{- $content := replace $content "<hr>" "<hr />" -}}
     <!-- Split the processed content by <hr /> tag -->
     {{- range (split $content "<hr />") -}}
       <!-- Only wrap in <section> tag if not already wrapped by shortcode -->

layouts/shortcodes/slide.html

@@ -8,6 +8,7 @@
     {{- $markdownContent = index $markdownContent $dataPath -}}
   {{- end -}}
   {{- $html := $markdownContent | markdownify -}}
+  {{- $html := replace $html "<hr>" "<hr />" -}}
   {{- $slides := split $html "<hr />" -}}
   {{- range $slides -}}
     {{- $scratch.Add "slides" . -}}