wait on rustfmt stable feature group_imports (rust-lang/rustfmt#5083)

Enable `group_imports` in [`rustfmt.toml`](https://github.com/jtmoon79/super-speedy-syslog-searcher/blob/0.0.32/rustfmt.toml#L11), tracking Issue https://github.com/rust-lang/rustfmt/issues/5083

https://rust-lang.github.io/rustfmt/?version=v1.5.1&search=#group_imports