Support WinZip AE-2 encryption

[tommaier123]

I have a zip that has some entries encrypted with AES-256 AE-2. I want to update the unencrypted values and leave the encrypted ones alone.
Currently this doesn't work because the vendor number is always set to AE-1 in ZipEntry.Write.cs line 450.
This causes the encrypted entries to become unreadable.

There are two possible solutions:

1. support SE-2 as a encryption format
2. read the vendor number and don't update it when saving the archive

[jshergal]

Thanks for reporting this bug/problem, and sorry about the delay in getting back to you. This is a self-service repository, where we merge PRs and where the merging of PRs causes nugets to be pushed automatically (if you bump the version number in your PR). I'll leave this issue open until someone (or yourself) fixes it.