Fix removeOne for internal set

[Guttz]

In the changed line, in go, if we assign a slice position to a variable, we'll have a copy.

ki.Start = v + 1, on line 218, was just modifying a copy, which is not what was intended to be done here.

If we get the reference as done in the change, we'll modify ki.Startproperly. Another option would be to reasign the copy to the array position. Either way, this should be fixed.

Simple test which would fail:

func (suite *IIntervalSetTestSuite) TestRemoveOne() {
	i := NewIntervalSet()
	i.addInterval(antlr.NewInterval(5, 10))

	i.removeOne(7)

	suite.Len(i.intervals, 2)
	suite.Equal(5, i.intervals[0].Start)
	suite.Equal(7, i.intervals[0].Stop)
	suite.Equal(8, i.intervals[1].Start)
	suite.Equal(10, i.intervals[1].Stop)
}