fix: make --edition 2021 visible in --help

Author: outloudvi

src/bin/main.rs

@@ -121,7 +121,7 @@ fn make_opts() -> Options {
          found reverts to the input file path",
         "[Path for the configuration file]",
     );
-    opts.optopt("", "edition", "Rust edition to use", "[2015|2018]");
+    opts.optopt("", "edition", "Rust edition to use", "[2015|2018|2021]");
     opts.optopt(
         "",
         "color",