Update pubspec.yaml and CHANGELOG.md.

Update changelog and pubspec

Fixed single byte update bug in keccak added regression tests.

3.4.0 release

Removed more references to AESFastEngine replaced with AESEngine.

Fixed bug in GCM counter (bcgit#142)
Fixed timing leakage in GCM (bcgit#140)

Ported AESEngine from BC java.

(See bcgit#141)
Deprecated aes_fast_engine and removed it from the provider look up.
Removed non-constant time comparison in base_aead_block_cipher.dart

Update for new version 3.3.5