logs: info not warn for no rollback

lib/workers/repository/process/lookup/rollback.js

@@ -16,7 +16,7 @@ function getRollbackUpdate(config, versions) {
   );
   // istanbul ignore if
   if (!lessThanVersions.length) {
-    logger.warn(
+    logger.info(
       { packageFile, depName, currentVersion },
       'Missing version has nothing to roll back to'
     );