build(deps): update futures-timer requirement from ^2.0 to ^3.0

Updates the requirements on [futures-timer](https://github.com/async-rs/futures-timer) to permit the latest version.
- [Release notes](https://github.com/async-rs/futures-timer/releases)
- [Commits](async-rs/futures-timer@2.0.1...v3.0.0)

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

heim-process/Cargo.toml

@@ -58,7 +58,7 @@ futures-executor = "^0.3"
 tokio = { version = "^0.2", features = ["rt-threaded"] }
 async-std = "^1.5"
 version-sync = "0.8"
-futures-timer = "^2.0"
+futures-timer = "^3.0"
 which = { version = "^3.1", default-features = false }
 
 [features]