Update changelog

Author: patrickkerrigan

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## [1.4.0] - 2022-01-09
+### Removed
+- Support for PHP 7.0 has now been removed, with PHP >=7.1 being required from this version onwards. Users who cannot use a newer version of PHP should continue to use 1.3.0, which will continue to receive security fixes for at least 12 months. Users who can use a newer version of PHP are strongly encouraged to upgrade to at least PHP 7.4
+
+### Fixed
+- Deprecation errors will no longer be triggered for the return type of `JsonSerializable::jsonSerialize()` under PHP >=8.1
+
 ## [1.3.0] - 2021-04-26
 ### Added
 - Allow setting aws.account_id for segments & subsegments