customizer: use the same license header as the main files.

docs/assets/js/src/customizer.js

@@ -14,7 +14,7 @@ window.onload = function () { // wait for load in a dumb way because B-0
   var cw = '/*!\n' +
            ' * Bootstrap v3.4.0 (http://getbootstrap.com)\n' +
            ' * Copyright 2011-' + new Date().getFullYear() + ' Twitter, Inc.\n' +
-           ' * Licensed under MIT (https://github.com/twbs/bootstrap/blob/master/LICENSE)\n' +
+           ' * Licensed under the MIT license\n' +
            ' */\n\n'
 
   var supportsFile = window.File && window.FileReader && window.FileList && window.Blob