Update goleveldb vendored dependency (see #662)

vendor/github.com/syndtr/goleveldb/leveldb/doc.go

@@ -8,6 +8,8 @@
 //
 // Create or open a database:
 //
+//	// The returned DB instance is safe for concurrent use. Which mean that all
+//	// DB's methods may be called concurrently from multiple goroutine.
 //	db, err := leveldb.OpenFile("path/to/db", nil)
 //	...
 //	defer db.Close()