fix s3 link (#1310)

tutorials/models/3_generative_model/5_dgmg.py

@@ -715,7 +715,7 @@ class DGMG(DGMGSkeleton):
 import torch.utils.model_zoo as model_zoo
 
 # Download a pre-trained model state dict for generating cycles with 10-20 nodes.
-state_dict = model_zoo.load_url('https://s3.us-east-2.amazonaws.com/dgl.ai/model/dgmg_cycles-5a0c40be.pth')
+state_dict = model_zoo.load_url('https://data.dgl.ai/model/dgmg_cycles-5a0c40be.pth')
 model = DGMG(v_max=20, node_hidden_size=16, num_prop_rounds=2)
 model.load_state_dict(state_dict)
 model.eval()

tutorials/models/4_old_wines/7_transformer.py

@@ -875,6 +875,6 @@ Transformer tutorial
 #
 # .. note::
 #     The notebook itself is not executable due to many dependencies.
-#     Download `7_transformer.py <https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/7_transformer.py>`__, 
+#     Download `7_transformer.py <https://data.dgl.ai/tutorial/7_transformer.py>`__, 
 #     and copy the python script to directory ``examples/pytorch/transformer`` 
 #     then run ``python 7_transformer.py`` to see how it works.

tutorials/models/5_giant_graph/1_sampling_mx.py

@@ -419,6 +419,6 @@ for nf in dgl.contrib.sampling.NeighborSampler(g, batch_size, num_neighbors,
 # advantages of this API are 1) simplicity, 2) allowing more system-level
 # optimization in the future.
 #
-# .. |image0| image:: https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/sampling/NodeFlow.png
-# .. |image1| image:: https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/sampling/sampling_result.png
+# .. |image0| image:: https://data.dgl.ai/tutorial/sampling/NodeFlow.png
+# .. |image1| image:: https://data.dgl.ai/tutorial/sampling/sampling_result.png
 #

tutorials/models/5_giant_graph/2_giant.py

@@ -356,7 +356,7 @@ Large-Scale Training of Graph Neural Networks
 # We can see that DGL can scale to graphs with up to 500M nodes and 25B
 # edges.
 #
-# .. |image0| image:: https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/sampling/arch.png
-# .. |image1| image:: https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/sampling/NUMA_speedup.png
-# .. |image2| image:: https://s3.us-east-2.amazonaws.com/dgl.ai/tutorial/sampling/whole_speedup.png
+# .. |image0| image:: https://data.dgl.ai/tutorial/sampling/arch.png
+# .. |image1| image:: https://data.dgl.ai/tutorial/sampling/NUMA_speedup.png
+# .. |image2| image:: https://data.dgl.ai/tutorial/sampling/whole_speedup.png
 #