build(deps): bump structopt from 0.3.20 to 0.3.21

Bumps [structopt](https://github.com/TeXitoi/structopt) from 0.3.20 to 0.3.21.
- [Release notes](https://github.com/TeXitoi/structopt/releases)
- [Changelog](https://github.com/TeXitoi/structopt/blob/master/CHANGELOG.md)
- [Commits](https://github.com/TeXitoi/structopt/compare/v0.3.20...v0.3.21)

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

Cargo.lock

@@ -2511,9 +2511,9 @@ checksum = "6446ced80d6c486436db5c078dde11a9f73d42b57fb273121e160b84f63d894c"
 
 [[package]]
 name = "structopt"
-version = "0.3.20"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "126d630294ec449fae0b16f964e35bf3c74f940da9dca17ee9b905f7b3112eb8"
+checksum = "5277acd7ee46e63e5168a80734c9f6ee81b1367a7d8772a2d765df2a3705d28c"
 dependencies = [
  "clap",
  "lazy_static",
@@ -2522,9 +2522,9 @@ dependencies = [
 
 [[package]]
 name = "structopt-derive"
-version = "0.4.13"
+version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "65e51c492f9e23a220534971ff5afc14037289de430e3c83f9daf6a1b6ae91e8"
+checksum = "5ba9cdfda491b814720b6b06e0cac513d922fc407582032e8706e9f137976f90"
 dependencies = [
  "heck",
  "proc-macro-error",

zebra-utils/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2018"
 publish = false
 
 [dependencies]
-structopt = "0.3.20"
+structopt = "0.3.21"
 color-eyre = "0.5.8"
 hex = "0.4"
 serde_json = "1.0"