build: bump clap from 2.34.0 to 3.0.0

Bumps [clap](https://github.com/clap-rs/clap) from 2.34.0 to 3.0.0.
- [Release notes](https://github.com/clap-rs/clap/releases)
- [Changelog](https://github.com/clap-rs/clap/blob/master/CHANGELOG.md)
- [Commits](https://github.com/clap-rs/clap/compare/v2.34.0...clap_complete-v3.0.0)

---
updated-dependencies:
- dependency-name: clap
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vhost_user_block/src/main.rs

@@ -23,7 +23,7 @@ fn main() {
         .author(crate_authors!())
         .about("Launch a vhost-user-blk backend.")
         .arg(
-            Arg::with_name("block-backend")
+            Arg::new("block-backend")
                 .long("block-backend")
                 .help(vhost_user_block::SYNTAX)
                 .takes_value(true)