Update connection.py

I have found that I couldn't assign a single value tuple without a trailing comma. If credentials is provided as `(app_id)` it ends up being turned in to a str (even if you explicitly cast it as a tuple) thus failing the tuple instance check. If you use `(app_id,)` everything works.

I added a check that will ensure it is a single value tuple by converting string to tuple (using the necessary trailing comma).

Author: kwollaston

O365/connection.py

@@ -365,6 +365,8 @@ def __init__(self, credentials, *, scopes=None,
          (client_id, client_secret)
         """
         if auth_flow_type == 'public':  # allow client id only for public flow
+            if isinstance(credentials, str): 
+                credentials = (credentials,)
             if not isinstance(credentials, tuple) or len(credentials) != 1 or (not credentials[0]):
                 raise ValueError('Provide client id only for public flow credentials')
         else: