Bump syn from 2.0.10 to 2.0.12 (#264)

Bumps [syn](https://github.com/dtolnay/syn) from 2.0.10 to 2.0.12.
- [Release notes](https://github.com/dtolnay/syn/releases)
- [Commits](dtolnay/syn@2.0.10...2.0.12)

---
updated-dependencies:
- dependency-name: syn
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

ctor/Cargo.toml

@@ -15,7 +15,7 @@ travis-ci = { repository = "mmastrac/rust-ctor", branch = "master" }
 quote = "1.0.20"
 
 [dependencies.syn]
-version = "2.0.10"
+version = "2.0.12"
 features = ["full", "parsing", "printing", "proc-macro"]
 default-features = false