doc: fix typo in TextEncoding section

PR-URL: #18201
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Weijia Wang <starkwang@126.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>

Author: yosuke-furukawa

doc/api/util.md

@@ -735,7 +735,7 @@ const uint8array = encoder.encode('this is some data');
 UTF-8 encodes the `input` string and returns a `Uint8Array` containing the
 encoded bytes.
 
-### textDecoder.encoding
+### textEncoder.encoding
 
 * {string}