Update structopt-derive to 0.4.18

Test: cd external/rust/crates && atest --host -c
Change-Id: I01c0867da7538adb52ee56fd3143c39d23fbf22c
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
index b41ac8a..e081f89 100644
--- a/Cargo.toml.orig
+++ b/Cargo.toml.orig
@@ -1,6 +1,6 @@
 [package]
 name = "structopt-derive"
-version = "0.4.16"
+version = "0.4.18"
 edition = "2018"
 authors = ["Guillaume Pinot <texitoi@texitoi.eu>"]
 description = "Parse command line argument by defining a struct, derive crate."