Fixed bottomJustify and middleJustify updates

In `updateBarJustify`, instead of the input parameter `justify`, the element's `this.justify` attribute was checked, preventing the attributes for `bottomJustify` and `middleJustify` from being updated. This complements fix #12.
Merge pull request #19 from idleherb/patch-1

Fixed bottomJustify and middleJustify updates