Css: Use only positive integers as values for widows/orphans

According to http://www.w3.org/TR/CSS2/page.html#propdef-orphans, widows
and orphans can take only positive integer values. Together with a Chrome 34
regression this caused the test to fail.

Fixes #15016
Closes gh-1563
Selector: Update Sizzle to 1.10.19

Fixes #14901
Fixes #14793