Bump deps to mitigate upstream vulnerabilities

This commit applies the changes from `cargo update` to the lockfile
in order to mitigate two vulnerabilities in upstream dependencies,
namely:

 - [RUSTSEC-2021-0056](https://rustsec.org/advisories/RUSTSEC-2021-0056)
 - [RUSTSEC-2021-0055](https://rustsec.org/advisories/RUSTSEC-2021-0055)

Author: jmcph4