onedrive authentication fails

[Louis Kirsch]

Trying to run a command with onedrive for the first time, e.g.
`duplicity list-current-files onedrive://backups`
triggers authentication correctly:
```
Could not load OAuth2 token. Trying to create a new one.
In order to authorize duplicity to access your OneDrive, please open XXX in a browser and copy the URL of the blank page the dialog leads to.
```

and then after submitting the URL of the blank page crashes with
```
Traceback (innermost last):
  File "/usr/local/bin/duplicity", line 1555, in <module>
    with_tempdir(main)
  File "/usr/local/bin/duplicity", line 1541, in with_tempdir
    fn()
  File "/usr/local/bin/duplicity", line 1380, in main
    action = commandline.ProcessCommandLine(sys.argv[1:])
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/duplicity/commandline.py", line 1127, in ProcessCommandLine
    globals.backend = backend.get_backend(args[0])
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/duplicity/backend.py", line 223, in get_backend
    obj = get_backend_object(url_string)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/duplicity/backend.py", line 209, in get_backend_object
    return factory(pu)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/duplicity/backends/onedrivebackend.py", line 90, in __init__
    self.initialize_oauth2_session()
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/duplicity/backends/onedrivebackend.py", line 157, in initialize_oauth2_session
    authorization_response=redirected_to)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/requests_oauthlib/oauth2_session.py", line 244, in fetch_token
    self._client.parse_request_body_response(r.text, scope=self.scope)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/oauthlib/oauth2/rfc6749/clients/base.py", line 409, in parse_request_body_response
    self.token = parse_token_response(body, scope=scope)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/oauthlib/oauth2/rfc6749/parameters.py", line 376, in parse_token_response
    validate_token_parameters(params)
  File "/usr/local/Cellar/duplicity/0.7.17/libexec/lib/python2.7/site-packages/oauthlib/oauth2/rfc6749/parameters.py", line 406, in validate_token_parameters
    raise w
 Warning: Scope has changed from "wl.skydrive_update wl.offline_access wl.skydrive" to "onedrive.readwrite wl.skydrive_update wl.offline_access wl.signin wl.skydrive".
```

Duplicity version: 0.7.17
Python version 2.7
OS Distro and version OSX
Type of target filesystem: OneDrive