brushlib: depend on gobject, not glib
brushlib: depend on gobject, not glib

Fix missing symbol during build: g_boxed_type_register_static

b3sigma/libmypaint,achadwick/libmypaint,b3sigma/libmypaint,b3sigma/libmypaint,achadwick/libmypaint,achadwick/libmypaint,achadwick/libmypaint