lib: remove useless default caught

The variable caught's value is undefined, so the '|| caught' is
useless.

PR-URL: #12884
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: JacksonTian

lib/internal/bootstrap_node.js

@@ -290,7 +290,7 @@
       var caught;
 
       if (process.domain && process.domain._errorHandler)
-        caught = process.domain._errorHandler(er) || caught;
+        caught = process.domain._errorHandler(er);
 
       if (!caught)
         caught = process.emit('uncaughtException', er);