Update Python client

Just so that nobody else has to do it.

Implements:
- [x] https://github.com/alphagov/notifications-python-client/pull/29

Which is a breaking change requiring the renaming of method arguments.

app/notify_client/provider_client.py

@@ -3,17 +3,17 @@ from app.notify_client import _attach_current_user
 
 
 class ProviderClient(BaseAPIClient):
-    def __init__(self, base_url=None, client_id=None, secret=None):
+    def __init__(self, base_url=None, service_id=None, api_key=None):
         super(self.__class__, self).__init__(
             base_url=base_url or 'base_url',
-            client_id=client_id or 'client_id',
-            secret=secret or 'secret'
+            service_id=service_id or 'service_id',
+            api_key=api_key or 'api_key'
         )
 
     def init_app(self, app):
         self.base_url = app.config['API_HOST_NAME']
-        self.client_id = app.config['ADMIN_CLIENT_USER_NAME']
-        self.secret = app.config['ADMIN_CLIENT_SECRET']
+        self.service_id = app.config['ADMIN_CLIENT_USER_NAME']
+        self.api_key = app.config['ADMIN_CLIENT_SECRET']
 
     def get_all_providers(self):
         return self.get(