build(deps): update pulldown-cmark requirement from 0.12.0 to 0.13.0

Updates the requirements on [pulldown-cmark](https://github.com/raphlinus/pulldown-cmark) to permit the latest version.
- [Release notes](https://github.com/raphlinus/pulldown-cmark/releases)
- [Commits](pulldown-cmark/pulldown-cmark@v0.12.0...v0.13.0)

---
updated-dependencies:
- dependency-name: pulldown-cmark
  dependency-type: direct:production
...

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

rinja_derive/Cargo.toml

@@ -20,7 +20,7 @@ proc-macro = true
 parser = { package = "rinja_parser", version = "=0.3.5", path = "../rinja_parser" }
 
 basic-toml = { version = "0.1.1", optional = true }
-pulldown-cmark = { version = "0.12.0", optional = true, default-features = false }
+pulldown-cmark = { version = "0.13.0", optional = true, default-features = false }
 serde = { version = "1.0", optional = true }
 serde_derive = { version = "1.0", optional = true }