test: refactor test-doctool-html.js

PR-URL: https://github.com/nodejs/node/pull/10696
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

test/doctool/test-doctool-html.js

@@ -74,7 +74,7 @@ const testData = [
   },
 ];
 
-testData.forEach(function(item) {
+testData.forEach((item) => {
   // Normalize expected data by stripping whitespace
   const expected = item.html.replace(/\s/g, '');
 

test/doctool/test-doctool-json.js

@@ -18,7 +18,7 @@ const json = require('../../tools/doc/json.js');
 // Test data is a list of objects with two properties.
 // The file property is the file path.
 // The json property is some json which will be generated by the doctool.
-var testData = [
+const testData = [
   {
     file: path.join(common.fixturesDir, 'sample_document.md'),
     json: {
@@ -136,10 +136,10 @@ var testData = [
   }
 ];
 
-testData.forEach(function(item) {
+testData.forEach((item) => {
-  fs.readFile(item.file, 'utf8', common.mustCall(function(err, input) {
+  fs.readFile(item.file, 'utf8', common.mustCall((err, input) => {
     assert.ifError(err);
-    json(input, 'foo', common.mustCall(function(err, output) {
+    json(input, 'foo', common.mustCall((err, output) => {
       assert.ifError(err);
       assert.deepStrictEqual(output, item.json);
     }));