doc: fix a code example in zlib.md

PR-URL: #31264
Reviewed-By: Luigi Pinca <[email protected]>
Reviewed-By: Colin Ihrig <[email protected]>
Reviewed-By: Gireesh Punathil <[email protected]>
Reviewed-By: David Carlier <[email protected]>
Reviewed-By: Ruben Bridgewater <[email protected]>
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Rich Trott <[email protected]>

doc/api/zlib.md

@@ -115,7 +115,7 @@ const fs = require('fs');
 http.createServer((request, response) => {
   const raw = fs.createReadStream('index.html');
   // Store both a compressed and an uncompressed version of the resource.
-  response.setHeader('Vary: Accept-Encoding');
+  response.setHeader('Vary', 'Accept-Encoding');
   let acceptEncoding = request.headers['accept-encoding'];
   if (!acceptEncoding) {
     acceptEncoding = '';