Fix typo in PROTOCOL.md

Should be `max`, not `min`.

Change-Id: Iec8d74b57bafee64e816f97a893ef18565c883a4

PROTOCOL.md

diff --git a/PROTOCOL.md b/PROTOCOL.md
index 5d13fae..2f3ee9b 100644
--- a/PROTOCOL.md
+++ b/PROTOCOL.md
@@ -10,7 +10,7 @@
 
 ```
 uint32 num_tags
-uint32 offsets[min(0, num_tags-1)]
+uint32 offsets[max(0, num_tags-1)]
 uint32 tags[num_tags]
 ```