feat: Upgrade default Node.js configuration to v12

BREAKING CHANGE:
Default Node.js configuration is set for Node.js v12
Projects which support Node.js v10 need to switch to `node/10`

Author: medikoo

node/10.js

@@ -0,0 +1,8 @@
+'use strict';
+
+const { join } = require('path');
+
+module.exports = {
+  extends: join(__dirname, 'index.js'),
+  globals: { globalThis: 'off' },
+};

node/6.js

@@ -3,7 +3,7 @@
 const { join } = require('path');
 
 module.exports = {
-  extends: join(__dirname, 'index.js'),
+  extends: join(__dirname, '10.js'),
   parserOptions: { ecmaVersion: 2015 },
   globals: { BigInt: 'off' },
 };

node/index.js

@@ -5,7 +5,7 @@ const { join } = require('path');
 module.exports = {
   // The only way to ensure that ESLint resolves expected config from any location
   extends: join(__dirname, '../index.js'),
-  globals: { BigInt: 'readonly' },
+  globals: { BigInt: 'readonly', globalThis: 'readonly' },
   env: { node: true },
   rules: {
     'no-path-concat': 'error',