use SDL2 port version 7

tools/ports/sdl.py

@@ -1,6 +1,6 @@
 import os, shutil, logging
 
-TAG = 'version_6'
+TAG = 'version_7'
 
 def get_with_configure(ports, settings, shared): # not currently used; no real need for configure on emscripten users' machines!
   if settings.USE_SDL == 2: