The markdown toolbar button tooltip is not using the default placement

Summary

The markdown toolbar button tooltip is not using the default placement. This affects the only haml version of the toolbar used in the wiki editor.

By default, tooltips are placed on top of the referring element.

See https://design.gitlab.com/components/tooltips.

Relevant logs and/or screenshots

Issues	Wiki

Possible fixes

This can be easily fixed by adding a placement attribute within the data options in the markdown_toolbar_button method.

diff --git a/app/helpers/markup_helper.rb b/app/helpers/markup_helper.rb
index 0d638b850b4..d598ee9c490 100644
--- a/app/helpers/markup_helper.rb
+++ b/app/helpers/markup_helper.rb
@@ -253,7 +253,7 @@ module MarkupHelper
   end

   def markdown_toolbar_button(options = {})
-    data = options[:data].merge({ container: 'body' })
+    data = options[:data].merge({ container: 'body', placement: 'top' })
     content_tag :button,
       type: 'button',
       class: 'toolbar-btn js-md has-tooltip',