Bump once_cell from 1.5.2 to 1.7.2 (#237)

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.5.2 to 1.7.2.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](matklad/once_cell@v1.5.2...v1.7.2)

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]

Cargo.lock

@@ -60,5 +60,5 @@ pretty_env_logger = "0.4.0"
 flate2 = "1.0"
 bincode = "1.3"
 tempfile = "3.2"
-once_cell = "1.4.1"
+once_cell = "1.7.2"
 dotenv = "0.15.0"