pkstrings: change write_fmt to write! like other places

Signed-off-by: Maxime “pep” Buquet <pep@bouah.net>

pkstrings/src/pkstring.rs

@@ -133,7 +133,7 @@ impl Deref for PKString {
 
 impl fmt::Display for PKString {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        f.write_fmt(format_args!("{:?}", &self.0))
+        write!(f, "{:?}", &self.0)
     }
 }