Update git2 requirement from 0.17.1 to 0.18.0 (#9)

Updates the requirements on [git2](https://github.com/rust-lang/git2-rs) to permit the latest version.
- [Changelog](https://github.com/rust-lang/git2-rs/blob/master/CHANGELOG.md)
- [Commits](rust-lang/git2-rs@0.17.1...git2-0.18.0)

---
updated-dependencies:
- dependency-name: git2
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Cargo.toml

@@ -22,7 +22,7 @@ serde_json = "1.0"
 chrono = "0.4"
 assert_cmd = "2.0.10"
 tempfile = "3.2.0"
-git2 = "0.17.1"
+git2 = "0.18.0"
 mockito = "1.0.2"
 csv = "1.1"
 log = "0.4"