Bump Portable.BouncyCastle from 1.8.6.7 to 1.8.8 (#498)
Bump Portable.BouncyCastle from 1.8.6.7 to 1.8.8 (#498)

Bumps [Portable.BouncyCastle](https://github.com/novotnyllc/bc-csharp) from 1.8.6.7 to 1.8.8.
- [Release notes](https://github.com/novotnyllc/bc-csharp/releases)
- [Commits](https://github.com/novotnyllc/bc-csharp/compare/pcl-v1.8.6.7...pcl-v1.8.8)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>

Co-authored-by: dependabot-preview[bot] <6a4c1c4838f800d1998274cd5234e1f65c55e90c@users.noreply.github.com>
rnwood/smtp4dev,rnwood/smtp4dev,rnwood/smtp4dev,rnwood/smtp4dev