build(deps): bump structopt from 0.3.15 to 0.3.16

Bumps [structopt](https://github.com/TeXitoi/structopt) from 0.3.15 to 0.3.16.
- [Release notes](https://github.com/TeXitoi/structopt/releases)
- [Changelog](https://github.com/TeXitoi/structopt/blob/master/CHANGELOG.md)
- [Commits](https://github.com/TeXitoi/structopt/commits)

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

Cargo.lock

@@ -2175,9 +2175,9 @@ checksum = "6446ced80d6c486436db5c078dde11a9f73d42b57fb273121e160b84f63d894c"
 
 [[package]]
 name = "structopt"
-version = "0.3.15"
+version = "0.3.16"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de2f5e239ee807089b62adce73e48c625e0ed80df02c7ab3f068f5db5281065c"
+checksum = "de5472fb24d7e80ae84a7801b7978f95a19ec32cb1876faea59ab711eb901976"
 dependencies = [
  "clap",
  "lazy_static",
@@ -2186,9 +2186,9 @@ dependencies = [
 
 [[package]]
 name = "structopt-derive"
-version = "0.4.8"
+version = "0.4.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "510413f9de616762a4fbeab62509bf15c729603b72d7cd71280fbca431b1c118"
+checksum = "1e0eb37335aeeebe51be42e2dc07f031163fbabfa6ac67d7ea68b5c2f68d5f99"
 dependencies = [
  "heck",
  "proc-macro-error",

zebra-utils/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 
 [dependencies]
 abscissa_core = "0.5"
-structopt = "0.3.15"
+structopt = "0.3.16"
 color-eyre = "0.5.0"
 hex = "0.4"
 serde_json = "1.0"