Update $icon-font-path to match bootstrap

Update the $icon-font-path to match the [default](https://github.com/twbs/bootstrap/blob/v3.2.0/less/variables.less#L76) in twbs/bootstrap, per #650.
This revision actually preserves exactly the whitespace in the less version ([link here](https://github.com/twbs/bootstrap/blob/v3.2.0/less/variables.less#L76)).