Expression optimize was wrong in 2.x.x

[hefangshi]

I update clean-css from 1.1.7 to 2.1.8, and found that the expression was optimized by mistake.

source:

.sample {
    zoom:1;
    _zoom:expression(function(el){el.firstChild.style.marginLeft=0;el.style.zoom="1"}(this))
}

clean-css 2.18 output:

.sample{zoom:1;_zoom:expression(function(el){el.firstChild.style.marginLeft=0;el.style.zoom="1"}

clean-css 1.17 output:

.sample{zoom:1;_zoom:expression(function(el){el.firstChild.style.marginLeft=0;el.style.zoom="1"}(this))}

[GoalSmashers]

Fixed in master. Will be included in upcoming 2.2 release.