Change CI minutes purchase to a primary action

ee/app/views/namespaces/pipelines_quota/_list.haml

@@ -9,7 +9,7 @@
         = link_to s_('UsageQuota|Buy additional minutes'),
         EE::SUBSCRIPTIONS_MORE_MINUTES_URL,
         target: '_blank',
-        class: 'btn btn-inverted btn-success float-right',
+        class: 'btn btn-success float-right',
         data: { track_event: 'click_buy_ci_minutes', track_label: namespace.actual_plan_name, track_property: 'pipeline_quota_page' }
 
   .row