Make easymde compatible with safari

core/templates/core/widgets/markdown_textarea.jinja

@@ -1,5 +1,5 @@
 <div>
-  <textarea is="markdown-input" name="{{ widget.name }}"{% include "django/forms/widgets/attrs.html" %}>{% if widget.value %}{{ widget.value }}{% endif %}</textarea>
+  <markdown-input name="{{ widget.name }}"{% include "django/forms/widgets/attrs.html" %}>{% if widget.value %}{{ widget.value }}{% endif %}</markdown-input>
 
   {# The easymde script can be included twice, it's safe in the code #}
   <script src="{{ statics.js }}" defer> </script>