Use to_string instead of format macro

Clippy emits:

  warning: useless use of `format!`

As suggested, use `to_string`.

Author: tcharding

src/lib.rs

@@ -186,7 +186,7 @@ impl MiniscriptKey for String {
     type Hash = String;
 
     fn to_pubkeyhash(&self) -> Self::Hash {
-        format!("{}", &self)
+        (&self).to_string()
     }
 }