Update socket2 requirement from 0.3.16 to 0.4.0 (#382)
Update socket2 requirement from 0.3.16 to 0.4.0 (#382)

Updates the requirements on [socket2](https://github.com/rust-lang/socket2) to permit the latest version.
- [Release notes](https://github.com/rust-lang/socket2/releases)
- [Changelog](https://github.com/rust-lang/socket2/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang/socket2/compare/v0.3.16...v0.4.0)

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

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