Updating the change log (#270)

Author: Isaiah Williams

CHANGELOG.md

@@ -33,6 +33,11 @@
 
 * Authentication
   * Addressed issue [#254](https://github.com/microsoft/Partner-Center-PowerShell/issues/254) with the [New-PartnerAccessToken](https://docs.microsoft.com/powershell/module/partnercenter/New-PartnerAccessToken) where the Scope parameter was incorrectly being required
+  * Addressed an issue where NullReferenceException exception was being encountered when invoking [Connect-PartnerCenter](https://docs.microsoft.com/powershell/module/partnercenter/Connect-PartnerCenter) using a certificate
+  * Addressed an issue where NullReferenceException exception was being encountered when invoking [New-PartnerAccessToken](https://docs.microsoft.com/powershell/module/partnercenter/New-PartnerAccessToken) using a certificate
+  * Defined the refresh token parameter set for the [New-PartnerAccessToken](https://docs.microsoft.com/powershell/module/partnercenter/New-PartnerAccessToken) command to make it easier to ensure all the appropriate parameters have been specified when exchanging a refresh token for an access token
+* Module
+  * All commands now perform operations asynchronously
 
 ## 3.0.4 - January 2020