Fix misuse of Math.random() in NEAT Crossover

* Math.random() returns a number in the range [0.0, 1.0) so the "mom"
  genome will always be picked
* A random number generator is readily available so make use of that
  rather than Math.random()
Merge pull request #183 from JayH5/random-fix

Fix misuse of Math.random() in NEAT Crossover