Send process_id in update_activity

This is now required as process activity branches have been merged

We now get this error on 0.2.0 workers when workers activity is enabled

2021-05-17 17:13:10,431 WARNING/arkindex_worker: Failed to update activity of element ba14aae2-3630-4b9c-9df3-717f0c613be9 to started due to an API error: {'process_id': ['This field is required.']}