Fix dropdownLinkColorActive to match original twitter/bootstrap

See https://github.com/twitter/bootstrap/blob/master/less/variables.less#L129 - must have been mistranslated. This was reported in thomas-mcdonald/bootstrap-sass#282
Merge pull request #53 from trisweb/trisweb_fix_dropdown_color_variable

Fix dropdownLinkColorActive to match original twitter/bootstrap