Update TORQUE_GAME_ENGINE_VERSION_STRING version number 4.0.0

Update TORQUE_GAME_ENGINE_VERSION_STRING version number to reflect current version 4.0
I somehow forgot to push this with my pull request #486 commit 6f52b8736035244b9faff4a67b9b815c7847b019

Engine/source/app/version.h

@@ -44,7 +44,7 @@
 #define TORQUE_GAME_ENGINE          4000
 
 /// Human readable engine version string.
-#define TORQUE_GAME_ENGINE_VERSION_STRING  "3.9.0"
+#define TORQUE_GAME_ENGINE_VERSION_STRING  "4.0.0"
 
 /// Gets the engine version number.  The version number is specified as a global in version.cc
 U32 getVersionNumber();