Changed help_string of --worker

It seems like 4 is the correct default value

Author: lorenzbaraldi

validate.py

@@ -66,7 +66,7 @@
 parser.add_argument('--model', '-m', metavar='NAME', default='dpn92',
                     help='model architecture (default: dpn92)')
 parser.add_argument('-j', '--workers', default=4, type=int, metavar='N',
-                    help='number of data loading workers (default: 2)')
+                    help='number of data loading workers (default: 4)')
 parser.add_argument('-b', '--batch-size', default=256, type=int,
                     metavar='N', help='mini-batch size (default: 256)')
 parser.add_argument('--img-size', default=None, type=int,