doc: fix typo in example code for util.styleText

Code shows how to style `errorMessage`, but then
only logs out `successMessage` twice. This might
trip people up when copying the code.

Author: rmehner

doc/api/util.md

@@ -1972,7 +1972,7 @@ const errorMessage = styleText(
   // Validate if process.stderr has TTY
   { stream: stderr },
 );
-console.error(successMessage);
+console.error(errorMessage);
 ```
 
 ```cjs