Apply proper sqrt on both sides in the proof of Perceptron Convergenc…

[mbriskar]

…e Theorem.

In the book, there is a conclusion that ||w(k)||^2 ≤ k.

Then later it is referred to sometimes as ||w(k)||^2 ≤ sqrt(k) and sometimes ||w(k)|| ≤ sqrt(k). Fixing this.