hgbook: en/undo-manual.dot annotate

hgbook

Fix typo

rev	line source
bos@124	1 digraph undo_manual {
bos@124	2 "first change" -> "second change";
bos@124	3 "second change" -> "third change";
bos@124	4 backout [label="back out\nsecond change", shape=box];
bos@124	5 "second change" -> backout;
bos@124	6 }