Update markdown.tmpl

Author: wxiaoguang

templates/repo/issue/fields/markdown.tmpl

@@ -1,3 +1,3 @@
 <div class="field {{if not .item.VisibleOnForm}}tw-hidden{{end}}">
-	<div>{{RenderMarkdownToHtml .Context .item.Attributes.value}}</div>
+	<div class="markup">{{RenderMarkdownToHtml .Context .item.Attributes.value}}</div>
 </div>