Use maintained forks of dotenv(->y) & memmap(->2).

[jsirois]

These 2 forks appear to be the blessed successors.

These unmaintained crate dependencies were revelead by a cargo audit run:

$ cargo audit
    Fetching advisory database from `https://github.com/RustSec/advisory-db.git`
      Loaded 570 security advisories (from /home/jsirois/.cargo/advisory-db)
    Updating crates.io index
    Scanning Cargo.lock for vulnerabilities (140 crate dependencies)
Crate:     dotenv
Version:   0.15.0
Warning:   unmaintained
Title:     dotenv is Unmaintained
Date:      2021-12-24
ID:        RUSTSEC-2021-0141
URL:       https://rustsec.org/advisories/RUSTSEC-2021-0141
Dependency tree:
dotenv 0.15.0
└── jump 0.12.0
    ├── scie-jump 0.12.0
    └── package 0.2.0

Crate:     memmap
Version:   0.7.0
Warning:   unmaintained
Title:     memmap is unmaintained
Date:      2020-12-02
ID:        RUSTSEC-2020-0077
URL:       https://rustsec.org/advisories/RUSTSEC-2020-0077
Dependency tree:
memmap 0.7.0
└── jump 0.12.0
    ├── scie-jump 0.12.0
    └── package 0.2.0

warning: 2 allowed warnings found