Updated SDL2 include files to fix Mac build in GitHub Actions

code/SDL2/include/SDL_config_minimal.h

@@ -1,6 +1,6 @@
 /*
   Simple DirectMedia Layer
-  Copyright (C) 1997-2017 Sam Lantinga <slouken@libsdl.org>
+  Copyright (C) 1997-2020 Sam Lantinga <slouken@libsdl.org>
 
   This software is provided 'as-is', without any express or implied
   warranty.  In no event will the authors be held liable for any damages
@@ -64,6 +64,9 @@ typedef unsigned long uintptr_t;
 /* Enable the stub haptic driver (src/haptic/dummy/\*.c) */
 #define SDL_HAPTIC_DISABLED 1
 
+/* Enable the stub sensor driver (src/sensor/dummy/\*.c) */
+#define SDL_SENSOR_DISABLED 1
+
 /* Enable the stub shared object loader (src/loadso/dummy/\*.c) */
 #define SDL_LOADSO_DISABLED 1