Change unixsocketperm comment to 700 from 755

According to unix manuals, "Connecting to the socket object requires
read/write permission." -- mode 755 is useless for anybody
other than the owner.

Fixes #1696

redis.conf

@@ -68,7 +68,7 @@ tcp-backlog 511
 # on a unix socket when not specified.
 #
 # unixsocket /tmp/redis.sock
-# unixsocketperm 755
+# unixsocketperm 700
 
 # Close the connection after a client is idle for N seconds (0 to disable)
 timeout 0