doc: reference signal(7) for the list of signals

Fixes: https://github.com/nodejs/node/issues/9309
PR-URL: https://github.com/nodejs/node/pull/9323
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>

doc/api/process.md

@@ -254,7 +254,7 @@ cases:
 <!--type=event-->
 <!--name=SIGINT, SIGHUP, etc.-->
 
-Emitted when the processes receives a signal. See sigaction(2) for a list of
+Emitted when the processes receives a signal. See sigaction(7) for a list of
 standard POSIX signal names such as `SIGINT`, `SIGHUP`, etc.
 
 Example of listening for `SIGINT`: