fix a type link

Author: coke

doc/Type/Proc/Async.rakudoc

@@ -476,7 +476,7 @@ multi method kill(Proc::Async:D: Int:D \signal)
 multi method kill(Proc::Async:D: Str:D \signal)
 
 Sends a signal to the running program. The signal can be a signal name
-("KILL" or "SIGKILL"), an integer (9) or an element of the C<Signal> enum
+("KILL" or "SIGKILL"), an integer (9) or an element of the L<C<Signal>|/type/Signal> enum
 (Signal::SIGKILL); by default and with no argument, the C<SIGHUP> signal will
 be used.