Range(start, count) behavior not corresponding with docs

[ospiper]

Describe the bug
According to the image of docs here, the second argument indicates length of the iterator (i.e. start ... (start+count-1)), but in code here the actual range gets to be start ... (start+count) which is not expected from the documentations.

To Reproduce

for i := range rxgo.Range(0, 3).Observe() {
	fmt.Println(i.V.(int))
}

outputs:

0
1
2
3

Expected behavior

0
1
2

[maguro]

PR filed #288.