Update rspirv requirement from 0.11 to 0.12 (#72)

Updates the requirements on [rspirv](https://github.com/gfx-rs/rspirv) to permit the latest version.
- [Release notes](https://github.com/gfx-rs/rspirv/releases)
- [Commits](gfx-rs/rspirv@rspirv-0.11.0+1.5.4...rspirv-0.12.0)

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

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Cargo.toml

@@ -28,4 +28,4 @@ winapi = { version = "0.3", features = ["wtypes", "oleauto", "combaseapi"] }
 libc = "0.2"
 
 [dev-dependencies]
-rspirv = "0.11"
+rspirv = "0.12"