fix boost API changes

Index: libs/s25main/network/GameClient.cpp
--- libs/s25main/network/GameClient.cpp.orig
+++ libs/s25main/network/GameClient.cpp
@@ -119,7 +119,7 @@ bool GameClient::HostGame(const CreateServerInfo& csi,
     if(playedMapPath != map_path)
     {
         boost::system::error_code ignoredEc;
-        copy_file(map_path, playedMapPath, boost::filesystem::copy_option::overwrite_if_exists, ignoredEc);
+        copy_file(map_path, playedMapPath, boost::filesystem::copy_options::overwrite_existing, ignoredEc);
     }
     return GAMESERVER.Start(csi, map_path, map_type, hostPw)
            && Connect("localhost", hostPw, csi.type, csi.port, true, csi.ipv6);
