Upgrade nix to 0.26

Remove the patch version in the dependency definition to get minor fixes
automatically. This shouldn't be a problem as nix should be API stable
across patch versions.

Signed-off-by: Richard Leitner <richard.leitner@skidata.com>

Cargo.toml

@@ -17,7 +17,7 @@ categories = ["hardware-support"]
 [target."cfg(unix)".dependencies]
 bitflags = "1.3.2"
 cfg-if = "1.0.0"
-nix = { version = "0.25.0", default-features = false, features = ["fs", "ioctl", "poll", "signal", "term"] }
+nix = { version = "0.26", default-features = false, features = ["fs", "ioctl", "poll", "signal", "term"] }
 
 [target.'cfg(all(target_os = "linux", not(target_env = "musl")))'.dependencies]
 libudev = { version = "0.3.0", optional = true }