Using ToLowerInvariant instead of ToLower (the game works for Turkish players now!)

http://www.moserware.com/2008/02/does-your-code-pass-turkey-test.html

Subsurface/Source/Screens/MainMenuScreen.cs

@@ -385,7 +385,7 @@ namespace Barotrauma
             XElement modeElement = null;
             foreach (XElement element in doc.Root.Elements())
             {
-                if (element.Name.ToString().ToLower() != "gamemode") continue;
+                if (element.Name.ToString().ToLowerInvariant() != "gamemode") continue;
 
                 modeElement = element;
                 break;