feat: add version flag

Cargo.lock

@@ -62,6 +62,7 @@ dependencies = [
  "atty",
  "bitflags",
  "indexmap",
+ "lazy_static",
  "os_str_bytes",
  "strsim",
  "termcolor",

Cargo.toml

@@ -1,5 +1,5 @@
 [dependencies]
-clap = "*"
+clap = { version = "*", features = ["cargo"] }
 indoc = "*"
 rand = "*"
 rayon = "*"

front/Cargo.lock

@@ -85,6 +85,7 @@ dependencies = [
  "atty",
  "bitflags",
  "indexmap",
+ "lazy_static",
  "os_str_bytes",
  "strsim",
  "termcolor",

src/cli.rs

@@ -1,6 +1,7 @@
 pub fn parse(args: Vec<String>) -> clap::ArgMatches {
     clap::App::new("Alejandra")
         .about("The Uncompromising Nix Code Formatter.")
+        .version(clap::crate_version!())
         .arg(
             clap::Arg::new("debug")
                 .help("Enable debug mode.")