wait on rustfmt stable feature imports_granularity (rust-lang/rustfmt#3349)

Enable `imports_granularity` in [`rustfmt.toml`](https://github.com/jtmoon79/super-speedy-syslog-searcher/blob/0.0.32/rustfmt.toml#L13), tracking Issue https://github.com/rust-lang/rustfmt/issues/4991

https://rust-lang.github.io/rustfmt/?version=v1.5.1&search=#imports_granularity