doc: update mode type for process.umask()

This commit updates the documentation for process.umask()
to reflect the fact that the mode option can be a string.

PR-URL: #31115
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/process.md

@@ -2297,7 +2297,7 @@ flag's behavior.
 added: v0.1.19
 -->
 
-* `mask` {number}
+* `mask` {string|integer}
 
 The `process.umask()` method sets or returns the Node.js process's file mode
 creation mask. Child processes inherit the mask from the parent process. Invoked