Fix a typo which raises an error

flaskbb/templates/management/forum_form.html

@@ -30,7 +30,7 @@
 
             {{ render_boolean_field(form.locked) }}
 
-            {{ horizontal_field(form.submit, div_class"col-lg-offset-0 col-lg-9") }}
+            {{ horizontal_field(form.submit, div_class="col-lg-offset-0 col-lg-9") }}
     </form>
 </div>
 {% endblock %}