Update instructions.md

Perhaps it was a typo but 4 is not the average of the list, nor the average of the first and last, while 5 is. So either the middle item should be 5 or the result should be `False`.

Author: chivalry

exercises/concept/card-games/.docs/instructions.md

@@ -76,7 +76,7 @@ Note: _The length of all hands are odd, to make finding a median easier._
 >>> approx_average_is_average([1, 2, 3])
 True
 
->>> approx_average_is_average([2, 3, 4, 8, 8])
+>>> approx_average_is_average([2, 3, 5, 8, 8])
 True
 
 >>> approx_average_is_average([1, 2, 3, 5, 9])