Fix missing comma

Author: Gymnasiast

src/openrct2-ui/windows/Dropdown.cpp

@@ -539,7 +539,7 @@ namespace OpenRCT2::Ui::Windows
         Colour::pesto,          Colour::asparagus,      Colour::pineGreen,    Colour::indigo,
         Colour::burntPink,
 
-        Colour::brown,          Colour::bordeauxRed,    Colour::salmonPink    Colour::lightBrown,
+        Colour::brown,          Colour::bordeauxRed,    Colour::salmonPink,   Colour::lightBrown,
         Colour::darkOliveGreen, Colour::oliveGreen,     Colour::darkGreen,    Colour::lightPurple,
         Colour::brightPink,