color: use inverse video for highlighting when there are no colors

When a terminal has no colors but has the ability to hide the cursor
(like a VT320), then using --bold would make a search match too hard
to see.

src/nano.c

@@ -2325,7 +2325,7 @@ int main(int argc, char **argv)
 		interface_color_pair[GUIDE_STRIPE] = A_REVERSE;
 		interface_color_pair[SCROLL_BAR] = A_NORMAL;
 		interface_color_pair[SELECTED_TEXT] = hilite_attribute;
-		interface_color_pair[HIGHLIGHTED] = hilite_attribute;
+		interface_color_pair[HIGHLIGHTED] = A_REVERSE;
 		interface_color_pair[PROMPT_BAR] = hilite_attribute;
 		interface_color_pair[STATUS_BAR] = hilite_attribute;
 		interface_color_pair[ERROR_MESSAGE] = hilite_attribute;