Fixed issue where caret wouldn't inherit "active" li style on nav-pills

Hi,

I've fixed a couple of issues:

- Caret wouldn't inherit "active" li style on nav-pills, which caused the caret to stay @link-color
- Corrected caret colour to '@link-hover-color' when a nav dropdown is ".open"

Not sure if the code is in the right place as I saw there is a "// Dropdowns" section at the end. Let me know if it needs correction.