Correction of EA and GA for nondeterministic fitness functions

[miraaitsaada]

Correction of an issue that occurs when the fitness function is nondeterministic (shuffled cross-validation for example). In the _select_n method, the total fitness is computed according to the stored fitnesses, but the probs variable is computed according to recalculated fitness values. This slight change makes the method use the stored fitnesses at each time, which solves the problem. This also makes the method run much faster (especially when the fitness function has a high complexity) by removing unnecessary calls to _fitness.