Update py-gobject3 to 3.4.2

- Fix marshalling of GByteArrays (Martin Pitt)
- Fix marshalling of ssize_t to smaller ints (Martin Pitt)
- Fix crash with GLib.child_watch_add (Daniel Narvaez) (#688067)
- Fix various bugs in GLib.IOChannel (Martin Pitt)
- Work around wrong 64 bit constants in GLib Gir (Martin Pitt)
- Fix OverflowError in source_remove() (Martin Pitt) (#684526)
- Fix Signal decorator to not use base class gsignals dict
  (Simon Feltman) (#686496)

(prlw1)