Fix bug in GIN Dataset degree OHE logic (#1498)

In the previous code, the same vector was being assigned to all the nodes in each graph.
`:` was used incorrectly assuming that only one row will be selected for each column but all rows were selected for each column.

python/dgl/data/gindt.py

@@ -237,7 +237,7 @@ class GINDataset(object):
             for g in self.graphs:
                 g.ndata['attr'] = np.zeros((
                     g.number_of_nodes(), len(label2idx)))
-                g.ndata['attr'][:, [label2idx[F.as_scalar(nl)] for nl in g.ndata['label']]] = 1
+                g.ndata['attr'][range(g.number_of_nodes()), [label2idx[F.as_scalar(nl)] for nl in g.ndata['label']]] = 1
 
         # after load, get the #classes and #dim
         self.gclasses = len(self.glabel_dict)