Give scrollbar pseudo-classes their own blocks, fixes issue #46

A bug in Chrome 25 on Lion requires each selector to have their own blocks. E.g. the following:

.antiscroll-inner::-webkit-scrollbar, .antiscroll-inner::scrollbar {...}

causes the width and height rules to be ignored by the browser resulting in both native and antiscroll scrollbars appearing at the same time.

Fixes issue #46