Modified RangedNumberGenerator in order to be compatible with random numbers that can be returned from the context

Now that in *v3.0* the default generator for numbers is the `RandomNumericSequenceGenerator`, there are times that the context can return a value which once gets added to the `Minimum` can result in an out-of-bounds result.

This Pull Request is related to #66. However, I am thinking that we could actually take advantage of the `RandomNumericSequenceGenerator` type inside the `RangedNumberGenerator`. That way this [method](https://github.com/AutoFixture/AutoFixture/blob/master/Src/AutoFixture/RangedNumberGenerator.cs#L68) could be simplified a lot since we could simply tell the `RandomNumericSequenceGenerator` instance to create a number inside the given range. This could be done as a separate work item after the *v3.0* is merged with *master*.