Weights are not updated in 3_net.py

[kvmanohar22]

In file 3_net.py, everything seems to go fine but the problem is, the weights w_h are not getting updated.
They have the same random values which were initialized at the beginning in all iterations of training.

In the first iteration, (only a subset of w_h and w_o values are printed )

Iteration: 1 Cost: 2.29556935362
w_h: [ 0.026779 -0.00800639 -0.01096162 -0.00354766 0.00137482] w_o: [-0.01249968 -0.00815679 0.01787239 -0.00080373 -0.00373115]

and in the 25th iteration
Iteration: 25 Cost: 2.24883255277
w_h: [ 0.026779 -0.00800639 -0.01096162 -0.00354766 0.00137482] w_o: [-0.0131051 -0.00619329 0.01693202 -0.00053586 -0.00538656]

This was not even the problem of sigmoid activation unit due to vanishing gradients because
same problem was faced even when tanh and ReLU activation units were used.