Fix linting error with 'import' keyword (#3929)

Author: allejo

.eslintrc.js

@@ -110,7 +110,7 @@ module.exports = {
     {
       files: ["tools/**/*.js"],
       parserOptions: {
-        ecmaVersion: 2018
+        ecmaVersion: 2020
       },
       rules: {
         camelcase: "off"

tools/lib/makestuff.js

@@ -5,7 +5,7 @@ const _ = require('lodash');
 const config = require("../build_config.js");
 
 async function clean(directory) {
-  let del = await import('del');
+  const del = await import('del');
   del.deleteSync([directory]);
   fs.mkdirSync(directory, { recursive: true });
 }