🚨 Implement Display for Cookie instead of ToString

```
error: direct implementation of `ToString`
   --> src/bus/cookies.rs:222:1
    |
222 | / impl ToString for Cookie {
223 | |     fn to_string(&self) -> String {
224 | |         format!("{} {} {}", self.id, self.created, self.cookie)
225 | |     }
226 | | }
    | |_^
    |
    = help: prefer implementing `Display` instead
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#to_string_trait_impl
    = note: `-D clippy::to-string-trait-impl` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(clippy::to_string_trait_impl)]`
```

src/bus/cookies.rs

@@ -1,13 +1,14 @@
 use anyhow::{anyhow, Error, Result};
 use rand::Rng;
-#[cfg(unix)]
-use std::{fs::Permissions, os::unix::prelude::PermissionsExt};
 use std::{
+    fmt::{self, Display, Formatter},
     io,
     str::FromStr,
     time::{Duration, SystemTime, UNIX_EPOCH},
 };
 #[cfg(unix)]
+use std::{fs::Permissions, os::unix::prelude::PermissionsExt};
+#[cfg(unix)]
 use tokio::fs::set_permissions;
 use tokio::{
     fs::{create_dir_all, metadata, remove_file, rename, File, OpenOptions},
@@ -219,9 +220,9 @@ impl FromStr for Cookie {
     }
 }
 
-impl ToString for Cookie {
-    fn to_string(&self) -> String {
-        format!("{} {} {}", self.id, self.created, self.cookie)
+impl Display for Cookie {
+    fn fmt(&self, f: &mut Formatter<'_>) -> fmt::Result {
+        write!(f, "{} {} {}", self.id, self.created, self.cookie)
     }
 }