Retrieve save and set back the auth issue

[embbnux]

In the docs, the getting auth data function should be var authData = await rcsdk.platform().auth().data();.
And in auth().setData() function, the code calculates the expire_time with expire_in data, we should not calculate that if expire_time is provided.

[embbnux]

We can also calculate the expire_time when expire_in provided. And developer can just remove the expire_in data when they set auth data as other RingCentral SDK