'Update the given device
Args:
user_id (str):
device_id (str):
content (dict): body of update request
Returns:
defer.Deferred:'

@defer.inlineCallbacks
def update_device(self, user_id, device_id, content):

    try:
        (yield self.store.update_device(user_id, device_id, new_display_name=content.get('display_name')))
        (yield self.notify_device_update(user_id, [device_id]))
    except errors.StoreError as e:
        if (e.code == 404):
            raise errors.NotFoundError()
        else:
            raise
