series: Make test cases more consistent

[mgw93]

This would fix issue #1047

[petertseng]

Based on the equation of length (series n xs) == min 0 (length xs - n + 1), these changes would make the exercise less consistent, not more. Therefore, we wouldn't want to accept them as-is.

We would want to take exactly one of the two following actions:

• Declare that n == 0 is an error. Therefore series be Int -> String -> Maybe [[Int]], and the result for n == 0 should be Nothing.
• Make the description better by submitting a pull request for https://github.com/exercism/problem-specifications/blob/main/exercises/series/description.md

[petertseng]

For series n xs, you would expect that length (series n xs) == min 0 (length xs - n + 1)

If n == 0 and length xs == 0, then length (series n xs) should be 0 - 0 + 1 == 1. This tells us that there is one way to make a series of length 0 from the empty series: the empty series. Therefore, the result should remain [[]] here.

[petertseng]

For series n xs, you would expect that length (series n xs) == min 0 (length xs - n + 1)

If n == 0 and length xs == 3, then length (series n xs) should be 3 - 0 + 1 == 4. Therefore, the result should remain [[],[],[],[]] here.