Depreciated net2 crate: Please release with upgraded mio dependencies

[getreu]

Solution: upgrade mio to 0.8.3

See the dependency tree below (cargo audit):

Crate:     net2
Version:   0.2.37
Warning:   unmaintained
Title:     `net2` crate has been deprecated; use `socket2` instead
Date:      2020-05-01
ID:        RUSTSEC-2020-0016
URL:       https://rustsec.org/advisories/RUSTSEC-2020-0016
Dependency tree:
net2 0.2.37
├── miow 0.2.2
│   └── mio 0.6.23
│       ├── notify 4.0.17
│       │   └── tp-note 1.17.0
│       └── mio-extras 2.0.6
│           └── notify 4.0.17
└── mio 0.6.23

[JohnTitor]

It's incorrect, see #413 (comment) and github/advisory-database#365.

[JohnTitor]

Well, it's different, sorry! But as I said in the above PR, v5 has upgraded it and we're going to make an official release soonish.