Bump once_cell from 1.8.0 to 1.9.0

Bumps [once_cell](https://github.com/matklad/once_cell) from 1.8.0 to 1.9.0.
- [Release notes](https://github.com/matklad/once_cell/releases)
- [Changelog](https://github.com/matklad/once_cell/blob/master/CHANGELOG.md)
- [Commits](https://github.com/matklad/once_cell/compare/v1.8.0...v1.9.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -47,7 +47,7 @@ ansi_colours = "^1.0"
 bincode = "1.0"
 console = "0.15.0"
 flate2 = "1.0"
-once_cell = "1.8"
+once_cell = "1.9"
 thiserror = "1.0"
 wild = { version = "2.0", optional = true }
 content_inspector = "0.2.4"