Himmelblau references in README.md

[jaakkor2]

Text and code refer to Hosaki's function but the math image is Himmelblau's function.

Later Himmelblau's function is referenced again

[jaakkor2]

Hosaki's function generated with https://www.codecogs.com/latex/eqneditor.php in gif format
f(x_1,x_2)=\left(1 - 8x_1 + 7x_1^2 - \frac{7}{3}x_1^3 + \frac{1}{4}x_1^4\right) x_2^2e^{-x_2}

[pkofod]

Oh, good catch :)