Mask OAuth credentials

[JCotton1123]

OAuth credentials are logged by default, example:

[2020-05-01T03:37:16.155Z] INFO Attempting login via OAuth2
[2020-05-01T03:37:16.171Z] INFO Making POST request to https://login.salesforce.com/services/oauth2/token with body {'grant_type': 'refresh_token', 'client_id': '...', 'client_secret': '...', 'refresh_token': '...'}
[2020-05-01T03:37:16.185Z] INFO OAuth2 login successful

Would you accept a PR to address this? Possibly by adding a parameter to, https://github.com/singer-io/tap-salesforce/blob/master/tap_salesforce/salesforce/__init__.py#L272, to mask the body, and updating, https://github.com/singer-io/tap-salesforce/blob/master/tap_salesforce/salesforce/__init__.py#L306, appropriately?