Update structopt-derive to 0.4.18

Test: cd external/rust/crates && atest --host -c
Change-Id: I01c0867da7538adb52ee56fd3143c39d23fbf22c
diff --git a/Android.bp b/Android.bp
index 2b0bac2..e008611 100644
--- a/Android.bp
+++ b/Android.bp
@@ -43,7 +43,7 @@
     name: "libstructopt_derive",
     crate_name: "structopt_derive",
     cargo_env_compat: true,
-    cargo_pkg_version: "0.4.16",
+    cargo_pkg_version: "0.4.18",
     srcs: ["src/lib.rs"],
     edition: "2018",
     rustlibs: [