clang-tidy: add ending namespace comments

Found with google-readability-namespace-comments

Signed-off-by: Rosen Penev <[email protected]>

taglib/tag.h

@@ -196,6 +196,6 @@ namespace TagLib {
     class TagPrivate;
     TagPrivate *d;
   };
-}
+}  // namespace TagLib
 
 #endif