Merge branch 'hide-graph-btn' into 'master'

Make toggle pipeline btn into button element

Toggle pipeline graph button was a `div` instead of a `button` ☹

See merge request !7404

app/views/projects/commit/_pipeline.html.haml

 .pipeline-graph-container
   .row-content-block.build-content.middle-block.pipeline-actions
     .pull-right
-      .btn.btn-grouped.btn-white.toggle-pipeline-btn
+      %button.btn.btn-grouped.btn-white.toggle-pipeline-btn
         %span.toggle-btn-text Hide
         %span pipeline graph
         %span.caret