[Key Vault] Update changelog for keys 4.4.0b4
# Release History
-## 4.4.0b4 (Unreleased)
+## 4.4.0b4 (2021-04-06)
+### Added
+- `CryptographyClient` can perform AES-CBCPAD encryption and decryption locally
+ ([#17762](https://github.com/Azure/azure-sdk-for-python/pull/17762))
-## 4.4.0b3 (2021-3-11)
+## 4.4.0b3 (2021-03-11)
### Added
- `CryptographyClient` will perform all operations locally if initialized with
the `.from_jwk` factory method
([#16565](https://github.com/Azure/azure-sdk-for-python/pull/16565))
- Added requirement for six>=1.12.0
-## 4.4.0b2 (2021-2-10)
+## 4.4.0b2 (2021-02-10)
### Fixed
- API versions older than 7.2-preview no longer raise `ImportError` when
performing async operations ([#16680](https://github.com/Azure/azure-sdk-for-python/pull/16680))
-## 4.4.0b1 (2021-2-10)
+## 4.4.0b1 (2021-02-10)
### Changed
- Key Vault API version 7.2-preview is now the default
- Updated msrest requirement to >=0.6.21
