doc: replace string with template string

PR-URL: https://github.com/nodejs/node/pull/17316
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Daijiro Wachi <daijiro.wachi@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Jon Moss <me@jonathanmoss.me>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/stream.md

@@ -764,7 +764,7 @@ available data. In the latter case, [`stream.read()`][stream-read] will return
 const fs = require('fs');
 const rr = fs.createReadStream('foo.txt');
 rr.on('readable', () => {
-  console.log('readable:', rr.read());
+  console.log(`readable: ${rr.read()}`);
 });
 rr.on('end', () => {
   console.log('end');