doc: use serial comma in buffer docs

Refs: #11321
Refs: #17384

PR-URL: #43048
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Akhil Marsonya <akhil.marsonya27@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

doc/api/buffer.md

@@ -134,7 +134,7 @@ console.log(Buffer.from('fhqwhgads', 'utf16le'));
 ```
 
 Node.js buffers accept all case variations of encoding strings that they
-receive. For example, UTF-8 can be specified as `'utf8'`, `'UTF8'` or `'uTf8'`.
+receive. For example, UTF-8 can be specified as `'utf8'`, `'UTF8'`, or `'uTf8'`.
 
 The character encodings currently supported by Node.js are the following: