bug fix (ProbitLikelihood)

@karlnapf 
merge the https://github.com/shogun-toolbox/shogun/pull/2248 PR first
then merge this PR
and finally merge the varational likelihoods https://github.com/shogun-toolbox/shogun/pull/2246

Note that ` src/shogun/mathematics/Statistics.cpp ` and ` src/shogun/mathematics/Statistics.h ` are fixed at https://github.com/shogun-toolbox/shogun/pull/2248