Fix clap deprecation warning

[Kedap]

When it was compiling I got:

warning: use of deprecated variant `clap::AppSettings::ArgRequiredElseHelp`: Replaced with `Command::arg_required_else_help` and `Command::is_arg_required_else_help_set`
  --> src/cli.rs:21:29
   |
21 | #[clap(setting(AppSettings::ArgRequiredElseHelp))]
   |                             ^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: `devmode` (bin "dm") generated 1 warning

This is because ArgRequiredElseHelp is deprecated as it says in the warning. As a solution, arg_required_else_help is used.

PS: Rustfmt was also applied