Bump nix from 0.20.0 to 0.21.0

Bumps [nix](https://github.com/nix-rust/nix) from 0.20.0 to 0.21.0.
- [Release notes](https://github.com/nix-rust/nix/releases)
- [Changelog](https://github.com/nix-rust/nix/blob/master/CHANGELOG.md)
- [Commits](https://github.com/nix-rust/nix/compare/v0.20.0...v0.21.0)

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

Cargo.lock

@@ -561,9 +561,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "libc"
-version = "0.2.94"
+version = "0.2.95"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "18794a8ad5b29321f790b55d93dfba91e125cb1a9edbd4f8e3150acc771c1a5e"
+checksum = "789da6d93f1b866ffe175afc5322a4d76c038605a1c3319bb57b06967ca98a36"
 
 [[package]]
 name = "libgit2-sys"
@@ -634,6 +634,15 @@ version = "2.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b16bd47d9e329435e309c58469fe0791c2d0d1ba96ec0954152a5ae2b04387dc"
 
+[[package]]
+name = "memoffset"
+version = "0.6.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "59accc507f1338036a0477ef61afdae33cde60840f4dfe481319ce3ad116ddf9"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.4.4"
@@ -646,14 +655,15 @@ dependencies = [
 
 [[package]]
 name = "nix"
-version = "0.20.0"
+version = "0.21.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "fa9b4819da1bc61c0ea48b63b7bc8604064dd43013e7cc325df098d49cd7c18a"
+checksum = "5c3728fec49d363a50a8828a190b379a446cc5cf085c06259bbbeb34447e4ec7"
 dependencies = [
  "bitflags",
  "cc",
  "cfg-if",
  "libc",
+ "memoffset",
 ]
 
 [[package]]

Cargo.toml

@@ -80,7 +80,7 @@ wait-timeout = "0.2.0"
 tempfile = "3.2.0"
 
 [target.'cfg(unix)'.dev-dependencies]
-nix = "0.20.0"
+nix = "0.21.0"
 
 [build-dependencies]
 clap = { version = "2.33", optional = true }