Bug Fix: n_layers_D should be 4

--n_layers_D should be 4 by default to match the setting described in the paper.

models/networks/discriminator.py

@@ -67,7 +67,7 @@ def forward(self, input):
 class NLayerDiscriminator(BaseNetwork):
     @staticmethod
     def modify_commandline_options(parser, is_train):
-        parser.add_argument('--n_layers_D', type=int, default=3,
+        parser.add_argument('--n_layers_D', type=int, default=4,
                             help='# layers in each discriminator')
         return parser