make the "formatting identity" comment a bit clearer (#39)

should close #37 by making the
debug message clearer
> File is already formatted correctly.
>
instead of
> File is formatted correctly.

cc/ @AucaCoyan

src/lib.rs

@@ -19,7 +19,7 @@ pub fn format_single_file(file: &PathBuf, config: &Config) {
  let formatted_bytes = add_newline_at_end_of_file(format_inner(&contents, config));
 
  if formatted_bytes == contents {
- debug!("File is formatted correctly.");
+ debug!("File is already formatted correctly.");
  }
 
  let mut writer = File::create(file).unwrap();