Fixed invite resend
Fixed invite resend

refs https://github.com/TryGhost/Ghost-Admin/commit/3d7e593c96993289d67d55a4b3152235715dcd2a

- `record.belongsTo().id` is an older Ember Data concept so it was returning `undefined`
- the `role` relationship is set up as `async: false` and is always output as an embedded record by our API so we're safe to use `this.role.id` without dealing with any async lookup

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