use fmt::Result where applicable

src/libstd/path.rs

@@ -1460,7 +1460,7 @@ impl<P: AsRef<Path>> iter::Extend<P> for PathBuf {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl fmt::Debug for PathBuf {
-    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
         fmt::Debug::fmt(&**self, formatter)
     }
 }