Bug 1622328 - .eslintrc.js: Add the license r=Standard8

Leave message empty to abort commit. HG: -- HG: user: Sylvestre Ledru
<sledru@mozilla.com> HG: branch 'default' HG: changed .eslintrc.js

Depends on D66801

Differential Revision: https://phabricator.services.mozilla.com/D66802

.eslintrc.js

@@ -1,3 +1,7 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
 "use strict";
 
 const xpcshellTestConfig = require("eslint-plugin-mozilla/lib/configs/xpcshell-test.js");