Update indoc requirement from 0.2.6 to 0.3.1

Updates the requirements on [indoc](https://github.com/dtolnay/indoc) to permit the latest version.
- [Release notes](https://github.com/dtolnay/indoc/releases)
- [Commits](https://github.com/dtolnay/indoc/commits/0.3.1)

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

Cargo.toml

@@ -39,7 +39,7 @@ skeptic = "0.13.3"
 [dev-dependencies]
 skeptic = "0.13.3"
 tempfile = "3.0.3"
-indoc = "0.2.6"
+indoc = "0.3.1"
 pretty_env_logger = "0.2.4"
 
 [package.metadata.docs.rs]