fix: let `sendOobCode` return errors

[MaxMonteil]

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Because of the void return in sendOobCode, errors are not propagated and cannot be caught and handles in the UI.

This happens when sending an oob code to reset a password on a non existing email.

import Auth from 'firebase-auth-lite';

const auth = new Auth({ apiKey });
auth.sendOobCode('PASSWORD_RESET', '[email protected]');

This change only removes the void keyword.

[GeKorm]

This also fixes await auth.sendOobCode() since it returns a Promise instead of undefined @samuelgozi