add func doTwoNumbersInArrayEqualK

[shandysiswandi]

@tlboright, i added a function for doTwoNumbersInArrayEqualK problem.

[nnashwin]

Hey @shandysiswandi thank you for contributing! I ran the function with the following values. It seems to return false when it should be true:

testVal := []int{4, 4, 1, 3, 1, 3, 2, 2, 5, 5, 1, 5, 2, 1, 2, 3, 5, 4}
doTwoNumbersInArrayEqualK(testVal, 2)