Allow variables within parenthesis

[hsandor]

Without space padding variables don't work within parentheses. If I pad them with spaces like this ( $url ) they work though.

GCSS:

$image-url: ../image/svg/footer.svg

$background-mixin($url)
  background-image: url($url)

#background
  $background-mixin($image-url)

EXPECTED:
#background{background-image:url(../image/svg/footer.svg);}

ACTUAL:
#background{background-image:url($url);}