Upgrade rust/crates/structopt to 0.3.18 am: e7bfadf396 am: b261218390 am: 0635f12c4a am: 7718ebe33b am: 10b9cd3290

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt/+/1436575

Change-Id: I29334e1e71cac6d140fed4549c3d5b9cff79aa53