cargo-fmt: Add --edition when printing the command

By mistake, it was forgotten to print out the edition in use when
printing the rustcmd command. Fix it.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

src/cargo-fmt/main.rs

@@ -341,6 +341,7 @@ fn run_rustfmt(
 
         if verbosity == Verbosity::Verbose {
             print!("rustfmt");
+            print!(" --edition {}", edition);
             fmt_args.iter().for_each(|f| print!(" {}", f));
             files.iter().for_each(|f| print!(" {}", f.display()));
             println!();