cli: Update to Rust 2021 edition

Author: Luni-4

rust-code-analysis-cli/Cargo.toml

@@ -3,7 +3,7 @@ name = "rust-code-analysis-cli"
 version = "0.0.23"
 authors = ["Calixte Denizet <cdenizet@mozilla.com>"]
 repository = "https://github.com/mozilla/rust-code-analysis/blob/master/rust-code-analysis-cli/"
-edition = "2018"
+edition = "2021"
 keywords = ["metrics"]
 description = "Tool to compute and export code metrics"
 license = "MPL-2.0"