In <=IE9, when line-heights are specified without units (i.e. line-height: 1.5;), IE returns 1.5 instead of the converted pixel value. In this cause, we should calculate the line-height ourselves based on the font-size.
Merge pull request #1 from joncampbell/master

In <=IE9, when line-heights are specified without units (i.e. line-heigh...