jcli: remove extern crate directives not required in Rust 2018
-extern crate bech32;
-extern crate chain_addr;
-extern crate chain_core;
-extern crate chain_crypto;
-extern crate chain_impl_mockchain;
-extern crate chain_time;
-extern crate gtmpl;
-extern crate hex;
-extern crate jormungandr_lib;
-extern crate mime;
-extern crate openapiv3;
-extern crate rand;
-extern crate rand_chacha;
-extern crate reqwest;
-extern crate serde;
-extern crate serde_json;
-extern crate serde_yaml;
-extern crate structopt;
-extern crate valico;
-
mod jcli_app;
use std::error::Error;
