Incorrect value in Noise.cs

[Zxynine]

In the noise class for 3d noise, it seems like your code was based off of code that contained a mistake in it. That mistake was later corrected and detailed within a paper on page 13 => https://weber.itn.liu.se/~stegu/simplexnoise/simplexnoise.pdf

your values of 0.6 should be 0.5

This may be why your function sometimes does not return a value between -1 and 1