fix(versioning): fix wrong this context (#4352)

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

@@ -35,7 +35,7 @@ function getRollbackUpdate(config, versions) {
     { dependency: depName, versions },
     'Versions found before rolling back'
   );
-  lessThanVersions.sort(version.sortVersions);
+  lessThanVersions.sort((a, b) => version.sortVersions(a, b));
   const toVersion = lessThanVersions.pop();
   // istanbul ignore if
   if (!toVersion) {