[Cargo.toml] bump structopt to v0.3.9

raw attributes were removed in TeXitoi/structopt#198

Author: chrissimpkins

Cargo.toml

@@ -23,7 +23,7 @@ pbr = "1.0.2"
 regex = "1.3.4"
 reqwest = "0.9"
 rustc_version = "0.2"
-structopt = "0.2.5"
+structopt = "0.3.9"
 tar = "0.4"
 tee = "0.1"
 tempdir = "0.3.6"