s2: Fix simple typo (interect to intersect)

[jonatasemidio]

On the cell_index_test.go file the error message from the verifyCellIndexContents method related to the intersect verification has a typo and writes interact instead intersect.

line:

geo/s2/cell_index_test.go

Line 217 in 740aa86

t.Errorf("%s: CellID does not interect the current range: %v <= %v && %v >= %v", desc, x.cellID.RangeMin(), r.LimitID().Prev(), x.cellID.RangeMax(), r.StartID())