CiphertextHeaders does not validate version

[mattsb42-aws]

CiphertextHeaders.parseVersion does not validate the version value.

https://github.com/aws/aws-encryption-sdk-java/blob/master/src/main/java/com/amazonaws/encryptionsdk/model/CiphertextHeaders.java#L163-L183

It should throw an error on any value other than (hex) 01.