Merge pull request #316 from moHani11/patch-1

Update README.md

lessons/3-NeuralNetworks/README.md

@@ -37,7 +37,7 @@ Thus, the simplest mathematical model of a neuron contains several inputs X<sub>
 
 where f is some non-linear **activation function**.
 
-> Early models of neuron were described in the classical paper [A logical calculus of the ideas immanent in nervous activity](http://www.springerlink.com/content/61446605110620kg/fulltext.pdf) by Warren McCullock and Walter Pitts in 1943. Donald Hebb in his book "[The Organization of Behavior: A Neuropsychological Theory](https://books.google.com/books?id=VNetYrB8EBoC)" proposed the way those networks can be trained.
+> Early models of neuron were described in the classical paper [A logical calculus of the ideas immanent in nervous activity](https://www.cs.cmu.edu/~./epxing/Class/10715/reading/McCulloch.and.Pitts.pdf) by Warren McCullock and Walter Pitts in 1943. Donald Hebb in his book "[The Organization of Behavior: A Neuropsychological Theory](https://books.google.com/books?id=VNetYrB8EBoC)" proposed the way those networks can be trained.
 
 ## In this Section