correct steam_api include files

Index: steam_achievements.cpp
--- steam_achievements.cpp.orig
+++ steam_achievements.cpp
@@ -1,8 +1,8 @@
 #include "steam_achievements.h"
 #include "achievement_id.h"
 
-#include "extern/steamworks/public/steam/isteamuserstats.h"
-#include "extern/steamworks/public/steam/isteamuser.h"
+#include "goldberg_emulator/steam/isteamuserstats.h"
+#include "goldberg_emulator/steam/isteamuser.h"
 
 SteamAchievements::SteamAchievements() {
   if (auto stats = SteamUserStats())
