crypto: convert to arrow function

Changed function expression to arrow function.

PR-URL: #24597
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

lib/internal/crypto/cipher.js

@@ -37,7 +37,7 @@ const { deprecate, normalizeEncoding } = require('internal/util');
 let StringDecoder;
 
 function rsaFunctionFor(method, defaultPadding) {
-  return function(options, buffer) {
+  return (options, buffer) => {
     const key = options.key || options;
     const padding = options.padding || defaultPadding;
     const passphrase = options.passphrase || null;