Fixed uci.edu dataset link (#2591)

Author: Daniel-Sinkin

chapter_optimization/minibatch-sgd.md

@@ -261,7 +261,7 @@ As we can see, the computation on the minibatch is essentially as efficient as o
 
 ## Reading the Dataset
 
-Let's have a look at how minibatches are efficiently generated from data. In the following we use a dataset developed by NASA to test the wing [noise from different aircraft](https://archive.ics.uci.edu/ml/datasets/Airfoil+Self-Noise) to compare these optimization algorithms. For convenience we only use the first $1,500$ examples. The data is whitened for preprocessing, i.e., we remove the mean and rescale the variance to $1$ per coordinate.
+Let's have a look at how minibatches are efficiently generated from data. In the following we use a dataset developed by NASA to test the wing [noise from different aircraft](https://archive.ics.uci.edu/dataset/291/airfoil+self+noise) to compare these optimization algorithms. For convenience we only use the first $1,500$ examples. The data is whitened for preprocessing, i.e., we remove the mean and rescale the variance to $1$ per coordinate.
 
 ```{.python .input}
 #@tab mxnet