Access to `Promise` methods in a way different from dot trigger `spec-only`

[zloirock]

Promise['all'];  // error  Avoid using non-standard 'Promise.undefined'  promise/spec-only
var method = 'all';
Promise[method]; // error  Avoid using non-standard 'Promise.method'     promise/spec-only

[zloirock]

Unlike #533, it can't be worked around by adding undefined or something like that to allowedMethods.