doc: fix process.stdout fd number

it should be 1 for the stdout fd number

PR-URL: #12055
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

Author: fmy

doc/api/process.md

@@ -1539,7 +1539,7 @@ must call `process.stdin.resume()` to read from it. Note also that calling
 * {Stream}
 
 The `process.stdout` property returns a [Writable][] stream connected to
-`stdout` (fd `2`).
+`stdout` (fd `1`).
 
 For example, to copy process.stdin to process.stdout: