Update `structopt` to `0.3`.

Cargo.lock

@@ -1,5 +1,7 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+version = 3
+
 [[package]]
 name = "adler32"
 version = "1.0.4"
@@ -1260,6 +1262,30 @@ dependencies = [
  "treeline",
 ]
 
+[[package]]
+name = "proc-macro-error"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
+dependencies = [
+ "proc-macro-error-attr",
+ "proc-macro2 1.0.8",
+ "quote 1.0.2",
+ "syn 1.0.14",
+ "version_check",
+]
+
+[[package]]
+name = "proc-macro-error-attr"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
+dependencies = [
+ "proc-macro2 1.0.8",
+ "quote 1.0.2",
+ "version_check",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "0.4.30"
@@ -1819,24 +1845,26 @@ checksum = "8ea5119cdb4c55b55d432abb513a0429384878c15dde60cc77b1c99de1a95a6a"
 
 [[package]]
 name = "structopt"
-version = "0.2.18"
+version = "0.3.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "16c2cdbf9cc375f15d1b4141bc48aeef444806655cd0e904207edc8d68d86ed7"
+checksum = "5277acd7ee46e63e5168a80734c9f6ee81b1367a7d8772a2d765df2a3705d28c"
 dependencies = [
  "clap",
+ "lazy_static 1.4.0",
  "structopt-derive",
 ]
 
 [[package]]
 name = "structopt-derive"
-version = "0.2.18"
+version = "0.4.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "53010261a84b37689f9ed7d395165029f9cc7abb9f56bbfe86bee2597ed25107"
+checksum = "5ba9cdfda491b814720b6b06e0cac513d922fc407582032e8706e9f137976f90"
 dependencies = [
  "heck",
- "proc-macro2 0.4.30",
- "quote 0.6.13",
- "syn 0.15.44",
+ "proc-macro-error",
+ "proc-macro2 1.0.8",
+ "quote 1.0.2",
+ "syn 1.0.14",
 ]
 
 [[package]]

Cargo.toml

@@ -30,7 +30,7 @@ serde_ignored = "0.0.4"
 serde_json = "1.0.26"
 strsim = "0.8.0"
 siphasher = "0.2.3"
-structopt = "0.2"
+structopt = "0.3"
 toml = "0.4"
 which = "2.0.0"
 binary-install = "0.0.2"