dg dataset in vlcs

[hopey233]

sorry to disturb you.

in my domain generalization task, i find a mistake in https://github.com/KaiyangZhou/Dassl.pytorch/blob/master/dassl/data/datasets/dg/vlcs.py#L40

because in the test data, it should inlcude all images in target domain, so it should be written as follows:

test = self._read_data(cfg.DATASET.TARGET_DOMAINS, "full")
test += self._read_data(cfg.DATASET.TARGET_DOMAINS, "test")