Fixed issue with sidebar button styling

app/views/shared/issuable/_sidebar.html.haml

@@ -5,7 +5,7 @@
     .block.issuable-sidebar-header
       %span.issuable-header-text.hide-collapsed.pull-left
         Todo
-      %button.gutter-toggle.pull-right.js-sidebar-toggle{ type: "button", aria: { label: "Toggle sidebar" } }
+      %a.gutter-toggle.pull-right.js-sidebar-toggle{ role: "button", href: "#", aria: { label: "Toggle sidebar" } }
         = sidebar_gutter_toggle_icon
       %button.btn.btn-default.issuable-header-btn.pull-right.js-issuable-todo{ type: "button", data: { todo_text: "Add Todo", mark_text: "Mark Done", id: (todo.id unless todo.nil?), url: issuable_todo_path(issuable) } }
         - if todo.nil?