Fix tf.keras.dataset.mnist/reuters np v1.16.3

This fix add `allow_pickle=True` to fix the numpy issue in 1.16.3.

See https://github.com/keras-team/keras/commit/34231971fa47cb2477b357c1a368978de4128294
and https://github.com/keras-team/keras/pull/12714

for related changes in keras-team/keras.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
diff --git a/tensorflow/python/keras/datasets/mnist.py b/tensorflow/python/keras/datasets/mnist.py
index 7e012c3..bbcdbea 100644
--- a/tensorflow/python/keras/datasets/mnist.py
+++ b/tensorflow/python/keras/datasets/mnist.py
@@ -48,7 +48,7 @@
       origin=origin_folder + 'mnist.npz',
       file_hash=
       '731c5ac602752760c8e48fbffcf8c3b850d9dc2a2aedcf2cc48468fc17b673d1')
-  with np.load(path) as f:
+  with np.load(path, allow_pickle=True) as f:
     x_train, y_train = f['x_train'], f['y_train']
     x_test, y_test = f['x_test'], f['y_test']