Disable default features of structopt

With this change we disable the default features of structopt. We try to
only pull in what is necessary and the program builds fine without the
default features enabled.

Cargo.toml

@@ -25,7 +25,7 @@ chrono = {version = "0.4", default-features = false}
 futures = {version = "0.3", default-features = false, features = ["async-await", "std"]}
 num-decimal = "0.2"
 serde_json = {version = "1.0", default-features = false}
-structopt = "0.3"
+structopt = {version = "0.3", default-features = false}
 tokio = {version = "0.2", default-features = false, features = ["rt-core"]}
 tracing = {version = "0.1", default-features = false, features = ["std"]}
 tracing-subscriber = {version = "0.1.6", default-features = false, features = ["ansi", "chrono", "env-filter", "fmt"]}