build: bump nix from 0.20.0 to 0.21.0 (#2773)

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>

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

Cargo.lock

@@ -777,9 +777,9 @@ dependencies = [
 
 [[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"
@@ -932,14 +932,15 @@ 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 1.2.1",
  "cc",
  "cfg-if 1.0.0",
  "libc",
+ "memoffset",
 ]
 
 [[package]]
@@ -1602,7 +1603,7 @@ dependencies = [
  "indexmap",
  "log",
  "native-tls",
- "nix 0.20.0",
+ "nix 0.21.0",
  "notify-rust",
  "once_cell",
  "open",

Cargo.toml

@@ -87,7 +87,7 @@ winapi = { version = "0.3.9", features = [
 ] }
 
 [target.'cfg(not(windows))'.dependencies]
-nix = "0.20.0"
+nix = "0.21.0"
 
 [build-dependencies]
 shadow-rs = "0.5.25"