A consecutive-run is a list of adjacent, consecutive integers. This list can be either increasing or decreasing. Create a function that takes an array of numbers and returns the length of the longest consecutive-run.
To illustrate:
longestRun([1, 2, 3, 5, 6, 7, 8, 9]) ➞ 5
// Two consecutive runs: [1, 2, 3] and [5, 6, 7, 8, 9] (longest).
longestRun([1, 2, 3, 10, 11, 15]) ➞ 3
// Longest consecutive-run: [1, 2, 3].
longestRun([5, 4, 2, 1]) ➞ 2
// Longest consecutive-run: [5, 4] and [2, 1].
longestRun([3, 5, 7, 10, 15]) ➞ 1
// No consecutive runs, so we return 1.
If there aren't any consecutive runs (there is a gap between each integer), return 1.