Release Notes:
- Fixed a (potential) small error in erf estimation. Technically, the
error is negligible.
I am not sure where the current calculation for erf come from and if it
is intended or a simple mistake. However it looks slightly different
from the official calculation, notably
[this](https://en.wikipedia.org/wiki/Error_function#Approximation_with_elementary_functions)
from Wikipedia.
I will add a comment if it is intended.
