buffer: fix typo in lib/buffer.js

PR-URL: nodejs#19126
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>

lib/buffer.js

@@ -742,7 +742,7 @@ Buffer.prototype.compare = function compare(target,
 // - buffer - a Buffer to search
 // - val - a string, Buffer, or number
 // - byteOffset - an index into `buffer`; will be clamped to an int32
-// - encoding - an optional encoding, relevant is val is a string
+// - encoding - an optional encoding, relevant if val is a string
 // - dir - true for indexOf, false for lastIndexOf
 function bidirectionalIndexOf(buffer, val, byteOffset, encoding, dir) {
   if (typeof byteOffset === 'string') {