jimtcl: build against SDL2

Upstream commit: https://github.com/msteveb/jimtcl/commit/3b834e42ee5887f85d10d7e50814b29d1b81a09f

jimtcl will automatically detect the sdl major version,
and adjust its header includes accordingly.
SDL1 is basically EOL, so SDL2 is preferrable when available.

pkgs/by-name/ji/jimtcl/package.nix

@@ -10,8 +10,8 @@
 
   sqlite,
   readline,
-  SDL,
-  SDL_gfx,
+  SDL2,
+  SDL2_gfx,
   openssl,
 
   SDLSupport ? true,
@@ -41,8 +41,8 @@ stdenv.mkDerivation (finalAttrs: {
       openssl
     ]
     ++ (lib.optionals SDLSupport [
-      SDL
-      SDL_gfx
+      SDL2
+      SDL2_gfx
     ]);
 
   configureFlags = [