Upgrade rust/crates/structopt to 0.3.18

Test: make
Change-Id: Ib5d515b0f5e9ac7fdd0f2f8e2f00ecf54dbf63ca
diff --git a/README.md b/README.md
index 48ac3c3..6609488 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,7 @@
-# StructOpt [![Build status](https://travis-ci.org/TeXitoi/structopt.svg?branch=master)](https://travis-ci.org/TeXitoi/structopt) [![](https://img.shields.io/crates/v/structopt.svg)](https://crates.io/crates/structopt) [![](https://docs.rs/structopt/badge.svg)](https://docs.rs/structopt)
+# StructOpt
+
+[![Build status](https://travis-ci.org/TeXitoi/structopt.svg?branch=master)](https://travis-ci.org/TeXitoi/structopt) [![](https://img.shields.io/crates/v/structopt.svg)](https://crates.io/crates/structopt) [![](https://docs.rs/structopt/badge.svg)](https://docs.rs/structopt)
+[![unsafe forbidden](https://img.shields.io/badge/unsafe-forbidden-success.svg)](https://github.com/rust-secure-code/safety-dance/)
 
 Parse command line arguments by defining a struct.  It combines [clap](https://crates.io/crates/clap) with custom derive.