docs(clipboard): fix an issue of demo code (#37438)

doc(clipboard): fix an issue of demo code

docs/api/clipboard.md

@@ -226,7 +226,7 @@ clipboard.writeBuffer('public/utf8-plain-text', buffer)
 
 const ret = clipboard.readBuffer('public/utf8-plain-text')
 
-console.log(buffer.equals(out))
+console.log(buffer.equals(ret))
 // true
 ```