[Beta] Correcting some styles for search selection dropdowns in menus

Hi There!

I was trying to add a <a href="http://beta.semantic-ui.com/modules/dropdown.html#search-selection">search selection dropdown</a> to an inverted menu and I noticed some of the dropdown background and text style for .ui.selection.dropdown was overriding the menu background and text colors. See this example: http://jsfiddle.net/vaL8phbw/8/

I took a crack at modifying menu.less to get the colors to be correct. I wasn't 100% sure whether these should go into menu.less or dropdown.less, but I put them in menu.less.

All suggestions & modifications welcome! Or let me know if I'm missing something and this isn't actually a bug.

Thanks!

Marc