Does not build in MacOS

Issue:
Does not build on Mac.

Error:
```
./src/main.zig:1:11: error: C import failed
const c = @cImport({
^
./zig-cache/o/812b576719d56fc816f68bf98065eb2d/cimport.h:1:10: note: 'SDL2/SDL.h' file not found
#include
^
./src/main.zig:7:9: note: referenced here
if (c.SDL_Init(c.SDL_INIT_VIDEO) != 0) {
^
```

Fix:
Change "SDL/SDL2" to "SDL2" in cImport.

Example of fix:
```
const c = @cImport({
@cInclude("SDL.h");
});
```