[IE11] JavaScript code uses Array.prototype.find(), which IE11 doesn't support

The accordions on Dashboard top page and APIs page don't work on IE11. The reason is JavaScript uses the prototype method IE11 doesn't support. The problematic function is Array.prototype.find() in https://github.com/3scale/system/blob/73c83d47cc01775b0f8a18ef9b57d9629fbb370a/assets/services/migrate.es6#L9

The error message:

—
Potentially unhandled rejection [1] TypeError: オブジェクトは 'find' プロパティまたはメソッドをサポートしていません。
at getCookieByKey (https://3scale-admin.app.oss.example.co.jp/assets/jspm-89c6417f92db51db2d9b009be4beaf94.js:480:225681)
at migrate (https://3scale-admin.app.oss.example.co.jp/assets/jspm-89c6417f92db51db2d9b009be4beaf94.js:480:225137)
at initialize (https://3scale-admin.app.oss.example.co.jp/assets/jspm-89c6417f92db51db2d9b009be4beaf94.js:480:226078)
at Anonymous function (https://3scale-admin.app.oss.example.co.jp/apiconfig/services:98:3)
...
—

The translation of the first line:

'Potentially unhandled rejection [1] TypeError: an object doesn't support 'find' property or method.'

MDN 'Browser compatibility' in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find explains this.

A possible workaround is https://github.com/babel/babel/issues/834 or using Array.find() (static method instead of prototype method)