Fix non-PCH build by adding an explicit include.

This used to build so the include of CStr.h disappeared from the include
chain at some point. PCH builds kept working because this file is
included in precompiled.h for the engine project.

Differential Revision: https://code.wildfiregames.com/D1273
Reviewed By: Imarok
This was SVN commit r21075.

source/ps/scripting/JSInterface_Mod.h

@@ -1,4 +1,4 @@
-/* Copyright (C) 2017 Wildfire Games.
+/* Copyright (C) 2018 Wildfire Games.
  * This file is part of 0 A.D.
  *
  * 0 A.D. is free software: you can redistribute it and/or modify
@@ -18,6 +18,7 @@
 #ifndef INCLUDED_JSI_MOD
 #define INCLUDED_JSI_MOD
 
+#include "ps/CStr.h"
 #include "scriptinterface/ScriptInterface.h"
 
 class ScriptInterface;