Update mio net2 deps in cargo.lock

[maxknv]

• Errors in rust-lang tests with fortanix-sgx-tools built from sources:

  11:29:23 ---- net::tcp::tests::bind_error stdout ----
  11:29:23 thread 'net::tcp::tests::bind_error' panicked at 'assertion failed: `(left == right)`
  11:29:23   left: `InvalidInput`,
  11:29:23  right: `AddrNotAvailable`', library/std/src/net/tcp/tests.rs:29:19

• They come from this tokio line: https://github.com/tokio-rs/tokio/blob/tokio-0.2.22/tokio/src/net/tcp/listener.rs#L138

• net2 and mio tokio's dependencies updated in lock file to solve this

Resolves #504

[jethrogb]

bors r+

[bors[bot]]

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• continuous-integration/travis-ci/push