Remove the backup prefix from the key

src/storage/s3.js

@@ -51,13 +51,15 @@ function getAllPaged(backupConfig, page, perPage, callback) {
             if (error) return callback(error);
 
             var results = data.Contents.map(function (backup) {
+                var key = backup.Key.slice(backupConfig.prefix.length + 1);
+
                 // This depends on the backups.js format of backup names :-(
-                var version = backup.Key.slice(backup.Key.lastIndexOf('-') + 2, -7);
+                var version = key.slice(key.lastIndexOf('-') + 2, -7);
 
                 return {
                     creationTime: backup.LastModified,
                     boxVersion: version,
-                    restoreKey: backup.Key,
+                    restoreKey: key,
                     dependsOn: []               // FIXME we have no information here
                 };
             });