* Bump SDL2 version in build dependencies script
* Use pre-release 2.7.1 for sdl_image
* Link for pre-releases is different
* sdl_image 2.8.0 has now been released
* Update kivy_deps.sdl2 and kivy_deps.sdl2-dev to 0.7.0 (to reflect the same changes made in Linux and macOS build scripts)