Fix error message for replica-serve-stale-data in redis.conf doc
seems that his piece of doc was always wrong (no such error in the code)
@@ -518,8 +518,9 @@ dir ./
# still reply to client requests, possibly with out of date data, or the
# data set may just be empty if this is the first synchronization.
#
-# 2) If replica-serve-stale-data is set to 'no' the replica will reply with
-# an error "SYNC with master in progress" to all commands except:
+# 2) If replica-serve-stale-data is set to 'no' the replica will reply with error
+# "MASTERDOWN Link with MASTER is down and replica-serve-stale-data is set to 'no'"
+# to all data access commands, excusing commands such as :
# INFO, REPLICAOF, AUTH, PING, SHUTDOWN, REPLCONF, ROLE, CONFIG, SUBSCRIBE,
# UNSUBSCRIBE, PSUBSCRIBE, PUNSUBSCRIBE, PUBLISH, PUBSUB, COMMAND, POST,
# HOST and LATENCY.
