Update HACKING

* HACKING: Update Swig requirement, as reported by Soheib.

HACKING

@@ -27,7 +27,7 @@ since the generated files they produce are distributed.)
   GNU Flex (the version seems to matters, we used 2.5.35)
   GNU Bison >= 2.7
   GNU Emacs (preferably >= 24 but it may work with older versions)
-  SWIG >= 2.0
+  SWIG >= 3.0 (for its better C++11 support)
   Doxygen >= 1.4.0
   Perl, with its Gettext module (it might be called something like
     liblocale-gettext-perl or p5-locale-gettext in your distribution)