update changelog

Author: Joel Butcher

CHANGELOG.md

@@ -5,12 +5,11 @@ Starting with version 5, the Facebook PHP SDK follows [SemVer](http://semver.org
 
 ## 6.x
 
-- 6.0.0 (2021-07-24)
-  - Migrated automated tests from Travis CI to Github Actions (#01d6a41)
-  - Added StyleCI as well as Scrutinizer for code style checks
-  - Bumped minimum PHP version requirement to 7.4, added PHP 8.0 (#8052aba)
-  - Updated minimum PHPUnit to version 9.3 (#8052aba)
-  - Reverted back to Mockery (1.0) over deprecated 'prophesize' (#8052aba)
+- Migrated automated tests from Travis CI to Github Actions (#01d6a41)
+- Added StyleCI as well as Scrutinizer for code style checks
+- Bumped minimum PHP version requirement to 7.4, added PHP 8.0 (#8052aba)
+- Updated minimum PHPUnit to version 9.3 (#8052aba)
+- Reverted back to Mockery (1.0) over deprecated 'prophesize' (#8052aba)
 
 ## 5.x