rustfmt: Use show_parse_errors

In rust-lang/rustfmt `hide_parse_errors` was changed to
`show_parse_errors`

Rename the variable and keep the default value `true`.

Author: jamillambert

rustfmt.toml

@@ -71,7 +71,7 @@ color = "Auto"
 unstable_features = false
 disable_all_formatting = false
 skip_children = false
-hide_parse_errors = false
+show_parse_errors = true
 error_on_line_overflow = false
 error_on_unformatted = false
 emit_mode = "Files"