Update a typo given in issues

The typo is specified in jikexueyuanwiki#143. Referencing https://github.com/tensorflow/tensorflow/blob/master/tensorflow/g3doc/tutorials/mnist/beginners/index.md

Author: terry182

SOURCE/tutorials/mnist/beginners/index.md

@@ -90,8 +90,7 @@ which digit a given image is of.
 For the purposes of this tutorial, we're going to want our labels
 as "one-hot vectors". A one-hot vector is a vector which is 0 in most
 dimensions, and 1 in a single dimension. In this case, the \\(n\\)th digit will be
-represented as a vector which is 1 in the \\(n\\)th dimensions. For example, 0
-would be \\([1,0,0,0,0,0,0,0,0,0,0]\\).
+represented as a vector which is 1 in the \\(n\\)th dimensions. For example, 3 would be \\([0,0,0,1,0,0,0,0,0,0]\\).
 Consequently, `mnist.train.labels` is a
 `[60000, 10]` array of floats.