Fixup comment in logger.fbs

Brian G. points out that we use "both" to describe 3 messages.

Change-Id: I03f573b05f3944136e058fd6f60e796906c73cdc
Signed-off-by: Austin Schuh <austin.schuh@bluerivertech.com>
diff --git a/aos/events/logging/logger.fbs b/aos/events/logging/logger.fbs
index 7d6eed4..0fe6253 100644
--- a/aos/events/logging/logger.fbs
+++ b/aos/events/logging/logger.fbs
@@ -132,7 +132,7 @@
   // case 3:  /u -> boot 0 received on boot 0.
   //          /r -> boot 1 received on boot 0.
   //          /u -> boot 1 received on boot 0.
-  //  We start logging after both messages arrive.
+  //  We start logging after all three messages arrive.
   //
   // case 4:  /u -> boot 0 received on boot 0.
   //          /r -> boot 1 received on boot 0.