Use asset pipeline if defined Sprockets instead of checking for Rails version
Update $dropdownLinkColorActive in _variables.scss

Update $dropdownLinkColorActive from $dropdownLinkColor to $white.

Reference Issue:
https://github.com/thomas-mcdonald/bootstrap-sass/issues/282
Merge pull request #286 from whatasunnyday/update-var-name

Update $dropdownLinkColorActive in _variables.scss
Merge pull request #284 from ssherif/master

Change the checks for Asset Pipeline from the
version of Rails to the presence of Sprockets