Fix dead_code warning

[nursoda]

This warning is shown compiling 0.14.0 on Arch:

warning: field `arg_version` is never read
  --> src/main.rs:36:5
   |
33 | struct Args {
   |        ---- field in this struct
...
36 |     arg_version: Option<String>,
   |     ^^^^^^^^^^^
   |
   = note: `Args` has a derived impl for the trait `Debug`, but this is intentionally ignored during dead code analysis
   = note: `#[warn(dead_code)]` on by default

It should be written without dead code.

[ChristophWurst]

https://github.com/ChristophWurst/krankerl/pull/963