upgrade buntdb

vendor/github.com/tidwall/buntdb/README.md

@@ -137,6 +137,7 @@ All keys/value pairs are ordered in the database by the key. To iterate over the
 err := db.View(func(tx *buntdb.Tx) error {
 	err := tx.Ascend("", func(key, value string) bool {
 		fmt.Printf("key: %s, value: %s\n", key, value)
+		return true // continue iteration
 	})
 	return err
 })