chore(deps): bump mongodb from 3.3.0 to 3.4.1 in /reference-apps/rust (#105)

Bumps [mongodb](https://github.com/mongodb/mongo-rust-driver) from 3.3.0 to 3.4.1.
- [Release notes](https://github.com/mongodb/mongo-rust-driver/releases)
- [Commits](mongodb/mongo-rust-driver@v3.3.0...v3.4.1)

---
updated-dependencies:
- dependency-name: mongodb
  dependency-version: 3.4.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]