🐛 Fix parameter handling in genSalt()

[cjduncana]

According to the documentation, the rounds parameter in genSalt() should have a default value of 10. What I understand by reading that is that if there is only the callback function as a parameter, then the function would assign the default value to rounds and the callback function provided to callback. The code was throwing an error when this was done.

I replaced the parameter handling inside genSalt() to deal with this situation.