make "break" required.

Signed-off-by: Shiwei Zhang <[email protected]>

Author: shizhMSFT

protocol.md

@@ -121,7 +121,7 @@ To verify a `(t, n)`-ENVELOPE:
     -   Verify SIGNATURE against PAE(UTF8(PAYLOAD_TYPE), SERIALIZED_BODY). Skip
         over if the verification fails.
     -   Add the accepted public key to the set ACCEPTED_KEYS.
-    -   Optionally, break if the cardinality of ACCEPTED_KEYS is greater or
+    -   Break if the cardinality of ACCEPTED_KEYS is greater or
         equal to `t`.
 -   Reject if the cardinality of ACCEPTED_KEYS is less than `t`.
 -   Reject if PAYLOAD_TYPE is not a supported type.