Rust 2018! (#726)

plume-cli/Cargo.toml

@@ -2,6 +2,7 @@
 name = "plume-cli"
 version = "0.4.0"
 authors = ["Plume contributors"]
+edition = "2018"
 
 [[bin]]
 name = "plm"

plume-cli/src/main.rs

@@ -1,8 +1,4 @@
-extern crate clap;
-extern crate diesel;
-extern crate dotenv;
-extern crate plume_models;
-extern crate rpassword;
+use dotenv;
 
 use clap::App;
 use diesel::Connection;