Correct RandomInt function

[andradei]

The RandomInt function says in the documentation that it can work with 3 arguments, but the function only uses 2, throwing an error if you ever use 3.

Passed more arguments than is possible : (3)

The documentation isn't the clearest either.

Reference from master:

https://github.com/bxcodec/faker/blob/master/faker.go#L1156