Update `travis-install-sdl2.sh` to download 2.0.9 tarball
set -xueo pipefail
-wget https://www.libsdl.org/release/SDL2-2.0.8.tar.gz -O sdl2.tar.gz
+wget https://www.libsdl.org/release/SDL2-2.0.9.tar.gz -O sdl2.tar.gz
tar xzf sdl2.tar.gz
pushd SDL2-* && ./configure && make && sudo make install && popd
wget -q https://www.libsdl.org/projects/SDL_ttf/release/SDL2_ttf-2.0.14.tar.gz
