Upgrade Rust Edition to 2021 (was 2015)

Cargo.toml

@@ -2,6 +2,7 @@
 name = "ui-compiler"
 version = "0.1.0"
 authors = ["Jáchym Toušek <enumag@gmail.com>"]
+edition = "2021"
 
 [dependencies]
 Inflector = "*"

src/main.rs

@@ -1,7 +1,3 @@
-extern crate inflector;
-extern crate log;
-extern crate simplelog;
-
 use std::env;
 use std::process::{Command, ExitCode};
 use std::fs;