Update memmap2 requirement from 0.3.0 to 0.4.0
Update memmap2 requirement from 0.3.0 to 0.4.0

Updates the requirements on [memmap2](https://github.com/RazrFalcon/memmap2-rs) to permit the latest version.
- [Release notes](https://github.com/RazrFalcon/memmap2-rs/releases)
- [Changelog](https://github.com/RazrFalcon/memmap2-rs/blob/master/CHANGELOG.md)
- [Commits](https://github.com/RazrFalcon/memmap2-rs/compare/v.0.3.0...v0.4.0)

---
updated-dependencies:
- dependency-name: memmap2
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
oschwald/maxminddb-rust