Fix a typo in the manpage

Signed-off-by: Stephane Glondu <steph@glondu.net>

babeld.man

@@ -48,7 +48,7 @@ sent on wired interfaces.  The default is 20 seconds.
 Enable detection of idle networks (networks on which we haven't received
 a hello packet in the last 5 minutes) and specify the interval in seconds
 at which scheduled hello packets are sent on idle interfaces.  This
-functonality is experimental, don't use it unless you know what you are
+functionality is experimental, don't use it unless you know what you are
 doing.
 .TP
 .BI \-k " priority"