Updating changelog

Author: aliabbasrizvi

CHANGELOG.md

@@ -7,7 +7,7 @@ July 9th, 2020
 * Introduced 2 APIs to interact with feature variables:
   * `get_feature_variable_json` allows you to get value for JSON variables related to a feature.
   * `get_all_feature_variables` gets values for all variables under a feature.
-* Added support for fetching authenticated datafiles. `HTTPProjectConfigManager` now accepts `datafileAccessToken` to be able to fetch datafiles belonging to secure environments.
+* Added support for fetching authenticated datafiles. `AuthDatafilePollingConfigManager` is a new config manager that allows you to poll for a datafile belonging to a secure environment. You can create a client by setting the `datafile_access_token`.
 
 ### Bug Fixes:
 * Fixed log messages for targeted rollouts evaluation. ([#268](https://github.com/optimizely/python-sdk/pull/268))