Fixes utf8cpp files paths

--- a/configure.ac.orig	2025-01-07 22:10:12.991524862 +0100
+++ b/configure.ac	2025-01-07 22:10:21.504672933 +0100
@@ -17,7 +17,7 @@ AC_PROG_CXX
 # Checks for header files.
 AC_CHECK_HEADER([cmath], [], [AC_MSG_ERROR([Your STL doesn't come with cmath, upgrade your libstdc++.])])
 AC_CHECK_HEADER([muParser.h], [], [AC_MSG_ERROR([Please install libmuparser >= 2.0.0 from http://muparser.beltoforion.de/])])
-AC_CHECK_HEADER([utf8.h], [], [AC_MSG_ERROR([Please install UTF8-CPP library from http://utfcpp.sourceforge.net/])])
+AC_CHECK_HEADER([utf8cpp/utf8.h], [], [AC_MSG_ERROR([Please install UTF8-CPP library from http://utfcpp.sourceforge.net/])])
 
 # Checks for typedefs, structures, and compiler characteristics.
 
--- a/src/server.cpp.orig	2025-01-07 22:10:29.541164708 +0100
+++ b/src/server.cpp	2025-01-07 22:10:35.551033920 +0100
@@ -30,7 +30,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <limits.h>
-#include <utf8.h>
+#include <utf8cpp/utf8.h>
 
 #include <string>
 
--- a/src/game.cpp.orig	2025-01-07 22:10:50.170715763 +0100
+++ b/src/game.cpp	2025-01-07 22:10:54.343958275 +0100
@@ -31,7 +31,7 @@
 #include <iostream>
 #include <fstream>
 
-#include <utf8.h>
+#include <utf8cpp/utf8.h>
 
 #include "auction.h"
 #include "card.h"