update changelog

CHANGELOG.md

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+# Changelog
+
+## [Unreleased]
+
+### Changed
+- tba.
+
+
+## [4.2.2](https://github.com/hapijs/catbox-mongodb/compare/v4.2.1...v4.2.2) - 2018-09-21
+
+### Added
+- Redis mock server for sentinel testing
+
+
+### Changed
+- refactor code to ES2015 class
+- refactor tests
+- update dependency: `ioredis v3 -> v4`
+- update dependency: `lab v15 -> v16`
+- update maintainer in readme
+
+
+## [4.2.1](https://github.com/hapijs/catbox-mongodb/compare/v4.2.0...v4.2.1) - 2018-09-07
+
+### Added
+- store boolean `false` values in the cache
+
+
+### Changed
+- removed `package-lock.json` from repository
+- extend readme on how to use a custom Redis client
+
+
+## [4.2.0](https://github.com/hapijs/catbox-mongodb/compare/v4.1.0...v4.2.0) - 2018-08-21
+
+### Added
+- `tls` options for Redis