Grammar fix

Doc/whatsnew/2.5.rst

@@ -2205,10 +2205,10 @@ Port-Specific Changes
 * MacOS X (10.3 and higher): dynamic loading of modules now uses the
   :cfunc:`dlopen` function instead of MacOS-specific functions.
 
-* MacOS X: a :option:`--enable-universalsdk` switch was added to the
+* MacOS X: an :option:`--enable-universalsdk` switch was added to the
   :program:`configure` script that compiles the interpreter as a universal binary
   able to run on both PowerPC and Intel processors. (Contributed by Ronald
-  Oussoren.)
+  Oussoren; :issue:`2573`.)
 
 * Windows: :file:`.dll` is no longer supported as a filename extension for
   extension modules.  :file:`.pyd` is now the only filename extension that will be