message: Fix incorrect help message
  The `cargo clean --target` command does not have a default setting, but the command-line help text says it does.
diff: @@ -7,7 +7,7 @@ pub fn cli() -> App {
  .about("Remove artifacts that cargo has generated in the past")
  .arg_package_spec_simple("Package to clean artifacts for")
  .arg_manifest_path()
  - .arg_target_triple("Target triple to clean output for (default all)")
  + .arg_target_triple("Target triple to clean output for")
  .arg_target_dir()
  .arg_release("Whether or not to clean release artifacts")
  .arg_doc("Whether or not to clean just the documentation directory")
  