Update data URL

CIFAR website is now using https.
Since urllib does not follow the http to https redirection and thus never retrieves any data, the data URL needs an update.

tutorials/image/cifar10/cifar10.py

@@ -78,7 +78,7 @@ INITIAL_LEARNING_RATE = 0.1       # Initial learning rate.
 # names of the summaries when visualizing a model.
 TOWER_NAME = 'tower'
 
-DATA_URL = 'http://www.cs.toronto.edu/~kriz/cifar-10-binary.tar.gz'
+DATA_URL = 'https://www.cs.toronto.edu/~kriz/cifar-10-binary.tar.gz'
 
 
 def _activation_summary(x):