Fix obsolete format traits.

They are to be removed from the language in the next rust upgrade.

components/gfx/font.rs

@@ -185,7 +185,7 @@ impl Font {
         let result = self.handle.get_table_for_tag(tag);
         let status = if result.is_some() { "Found" } else { "Didn't find" };
 
-        debug!("{:s} font table[{:s}] with family={}, face={}",
+        debug!("{} font table[{}] with family={}, face={}",
                status, tag.tag_to_str(),
                self.handle.family_name(), self.handle.face_name());