Replaces btn-transparent with btn-default-tertiary

app/views/shared/_label.html.haml

@@ -26,7 +26,7 @@
           %button{ type: 'button', class: 'btn gl-button btn-default-tertiary btn-sm js-label-options-dropdown', data: { toggle: 'dropdown' }, aria_label: _('Label actions dropdown') }
             = sprite_icon('ellipsis_v')
                 %li
-                  %button.js-promote-project-label-button.gl-button.btn.btn-default.btn-transparent{ disabled: true, type: 'button',
+                  %button.js-promote-project-label-button.gl-button.btn.btn-default-tertiary{ disabled: true, type: 'button',
                     data: { url: promote_project_label_path(label.project, label),
                             label_title: label.title,
                             label_color: label.color,