Use dropdown hover colors instead of active colors

In a Bootstrap 3 dropdown, an item's hover/focus state  has a light gray
background (@dropdown-link-hover-bg) with dark gray text
(@dropdown-link-hover-color).

See https://github.com/twbs/bootstrap/blob/master/less/dropdowns.less#L73-L81
Update expected hover background color in test

Forgot to include this in 86d8304e4f5afb430ace91b7f68cb1337c1458db.
Merge pull request #6 from jeffbowen/master

Use dropdown hover colors instead of active colors