Navbar toggle is not vertically aligned (3.0.0-wip) with custom navbar height

When using navbars higher than the default one, the navbar-toggle button is not centered.

Fiddle demonstrating this issue (compiled with `@navbar-height: 60px;`): http://jsfiddle.net/tagliala/mRVMe/2/

Another fiddle with the proposed fix: http://jsfiddle.net/tagliala/mRVMe/3/