Use button groups in build summary for consistency

app/views/projects/builds/show.html.haml

@@ -113,7 +113,8 @@
         %h4.title
           Build ##{@build.id}
           - if can?(current_user, :update_build, @project)
-            .pull-right
+            .center
+              .btn-group{ role: :group }
                 - if @build.cancel_url
                   = link_to "Cancel", @build.cancel_url, class: 'btn btn-sm btn-danger', method: :post
                 - elsif @build.retry_url