build(deps): update redox_syscall requirement from 0.3 to 0.4 (#256)

Updates the requirements on redox_syscall to permit the latest version.

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

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

Cargo.toml

@@ -31,7 +31,7 @@ features = [
 ]
 
 [target.'cfg(target_os = "redox")'.dependencies]
-redox_syscall = "0.3"
+redox_syscall = "0.4"
 
 [dev-dependencies]
 doc-comment = "0.3"