authorization_url doesn't use callback_uri provided during initialisation

[sgabello]

An example using an explicit callback URI.

>>> request_token_url = 'https://api.twitter.com/oauth/request_token'
>>> authorization_url = 'https://api.twitter.com/oauth/authorize'
>>> oauth_session = OAuth1Session('client-key', client_secret='secret', callback_uri='https://127.0.0.1/callback')
>>> oauth_session.fetch_request_token(request_token_url)
{
    'oauth_token': 'sdf0o9823sjdfsdf',
    'oauth_token_secret': '2kjshdfp92i34asdasd',
}
>>> oauth_session.authorization_url(authorization_url)

should return:
https://api.twitter.com/oauth/authorize?oauth_token=sdf0o9823sjdfsdf&oauth_callback=https%3A%2F%2F127.0.0.1%2Fcallback
And instead it returns:
https://api.twitter.com/oauth/authorize?oauth_token=sdf0o9823sjdfsdf