Upgrade to ECMAScript 2020

This is needed in order to use `globalThis`, see #1894.

Author: jaylinski

.eslintrc.js

@@ -1,17 +1,16 @@
 module.exports = {
   extends: ['eslint:recommended', 'plugin:compat/recommended', 'prettier'],
   globals: {
-    self: false
+    self: false,
   },
   env: {
     node: true,
-    es2017: true
+    es2020: true,
   },
   parserOptions: {
-    sourceType: 'module'
+    sourceType: 'module',
   },
   rules: {
-    // TODO check if redundant rules
     'no-console': 'warn',
 
     // temporarily disabled until the violating places are fixed.
@@ -60,6 +59,6 @@ module.exports = {
 
     // ECMAScript 6 //
     //--------------//
-    'no-var': 'error'
-  }
+    'no-var': 'error',
+  },
 };

README.markdown

@@ -79,7 +79,7 @@ There are a few Mustache behaviors that Handlebars does not implement.
 Supported Environments
 ----------------------
 
-Handlebars has been designed to work in any ECMAScript 2017 environment. This includes
+Handlebars has been designed to work in any ECMAScript 2020 environment. This includes
 
 - Node.js
 - Chrome