Docs: Corrected typo in the basics of PE page, maths section.
I corrected a small typo in the basics of PE page, maths section. The parenthesis containing the squared exponent should read (y_i - (t_i * m + c)) instead of (y_i - (t_i * x + c)) for a model H defined by y = m*x + c.
Edited by Sumeet Kulkarni