style(text): Avoid unnecessary getBoundingClientRect() calls
style(text): Avoid unnecessary getBoundingClientRect() calls

May seem like useless micro optimization, but just with this simple change my sizable graph redraw went from 6s to 3s.
Each call to getBoundingClientRect() causes forced layout, avoiding when possible can make big difference.

Close #11

naver/billboard.js,naver/billboard.js,naver/billboard.js,naver/billboard.js