Minor documentation fix for BaseClient
Minor documentation fix for BaseClient

The type field for the `authorizer` arg to BaseClient construction was
malformed. As a result, it was not rendering as a sphinx link.

globusonline/globus-sdk-python,globus/globus-sdk-python,aaschaer/globus-sdk-python,globus/globus-sdk-python,sirosen/globus-sdk-python