doc: fix broken internal link in process.md

PR-URL: #10828
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Daniel Bevenius <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Jeremiah Senkpiel <[email protected]>
Reviewed-By: James M Snell <[email protected]>

Author: addaleax

doc/api/process.md

@@ -1754,5 +1754,5 @@ cases:
 [Readable]: stream.html
 [Child Process]: child_process.html
 [Cluster]: cluster.html
-[`process.exitCode`]: #processexitcode-1
+[`process.exitCode`]: #process_process_exitcode
 [LTS]: https://github.com/nodejs/LTS/