ci: fix Pulish stage by using getBuildType()

Signed-off-by: Jakub Sokołowski <jakub@status.im>

ci/Jenkinsfile.combined

@@ -81,7 +81,7 @@ pipeline {
     stage('Publish') {
       when { expression { params.PUBLISH } }
       steps { script {
-        switch (btype) {
+        switch (utils.getBuildType()) {
           case 'nightly': /* Create JSON file with newest build URLs */
             s3.updateBucketJSON(urls, 'latest.json');
             break;