[[CHORE]] Recognize 'esversion: 11'

This commit extends the options parsing system to tolerate the values
"11" and "2020" for the `esversion` linting option. It does not
introduce support for any features introduced by the new edition of the
language.

src/jshint.js

@@ -710,6 +710,7 @@ var JSHINT = (function() {
           case "8":
           case "9":
           case "10":
+          case "11":
             state.option.moz = false;
             state.option.esversion = +val;
             break;
@@ -718,6 +719,7 @@ var JSHINT = (function() {
           case "2017":
           case "2018":
           case "2019":
+          case "2020":
             state.option.moz = false;
             // Translate specification publication year to version number.
             state.option.esversion = +val - 2009;

src/options.js

@@ -1051,6 +1051,7 @@ exports.val = {
    *  - `10` - To enable language features introduced by ECMAScript
    *    10](https://www.ecma-international.org/ecma-262/10.0/index.html).
    *    Notable additions: optional catch bindings.
+   *  - `11` - To enable language features introduced by ECMAScript 11.
    */
   esversion: 5
 };

src/state.js

@@ -65,6 +65,15 @@ var state = {
     return this.option.moz;
   },
 
+  /**
+   * Determine if constructs introduced in ECMAScript 11 should be accepted.
+   *
+   * @returns {boolean}
+   */
+  inES11: function() {
+    return this.esVersion >= 11;
+  },
+
   /**
    * Determine if constructs introduced in ECMAScript 10 should be accepted.
    *

tests/test262/test.js

@@ -51,7 +51,7 @@ module.exports = function(test) {
 
   try {
     JSHint(test.contents, {
-      esversion: 10,
+      esversion: 11,
       maxerr: Infinity,
       module: isModule,
       unstable: {

tests/unit/options.js

@@ -4238,13 +4238,15 @@ exports.esversion = function(test) {
     "// jshint esversion: 10",
     "// jshint esversion: 2019",
     "// jshint esversion: 11",
-    "// jshint esversion: 2020"
+    "// jshint esversion: 2020",
+    "// jshint esversion: 12",
+    "// jshint esversion: 2021"
   ];
 
   TestRun(test, "Value")
     .addError(2, 1, "Bad option value.")
-    .addError(14, 1, "Bad option value.")
-    .addError(15, 1, "Bad option value.")
+    .addError(16, 1, "Bad option value.")
+    .addError(17, 1, "Bad option value.")
     .test(code);
 
   var es5code = [