[Ubuntu] change mouse scrolling between standard and natural

Standard: 

sudo vi .Xmodmap

insert the content as below

pointer = 1 2 3 4 5  6 7 8 9 10 11 12

Natural:

sudo vi .Xmodmap

insert the content as below

pointer = 1 2 3 5 4 6 7 8 9 10 11 12

Have fun with Ubuntu!