man: ip-route: Make synopsis consistent with description

While the synopsis section contains 'ip route list', it is later
described as 'ip route show'. Make this consistent by replacing 'list'
with 'show' in synopsis.
Signed-off-by: Phil Sutter <phil@nwl.cc>

man/man8/ip-route.8.in

@@ -16,7 +16,7 @@ ip-route \- routing table management
 
 .ti -8
 .BR "ip route" " { "
-.BR list " | " flush " } "
+.BR show " | " flush " } "
 .I  SELECTOR
 
 .ti -8