application icons – Android Shape Shifter

If anyone here is familiar with the Android form change tool, I need help for a trivial task. I'm trying to change a plus icon to a minus icon, exactly the opposite of what most tutorials show and its past hours, but I have not been able to do it.

It's pretty easy to imagine what I want to do. Basically, I want both ends of the vertical line of the plus icon to collapse in the center … as simple as that.

Could someone just break the steps? or point to a similar example

icons –

That's where I'm stuck … I just matched the two horizontal lines, but the vertical lines now act in a strange way. screen.