Add missing include in AColor.cpp

Adds include for copy_n in AColor.cpp to fix issues with
compiling on some Linux-based systems.

Signed-off-by: akleja <storspov@gmail.com>
Reference-to: https://github.com/tenacityteam/tenacity/pull/663

src/AColor.cpp

@@ -22,6 +22,7 @@ It is also a place to document colour usage policy in Audacity
 #include "AColorResources.h"
 
 
+#include <algorithm>
 #include <wx/window.h>
 #include <wx/colour.h>
 #include <wx/dc.h>