Bump to latest version of SDL2_mixer in CI

Author: johnthagen

.travis.yml

@@ -13,7 +13,7 @@ install:
 - 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
 - wget -q https://www.libsdl.org/projects/SDL_image/release/SDL2_image-2.0.1.tar.gz
-- wget -q https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-2.0.1.tar.gz
+- wget -q https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-2.0.2.tar.gz
 - wget -q -O SDL2_gfx-1.0.1.tar.gz https://sourceforge.net/projects/sdl2gfx/files/SDL2_gfx-1.0.1.tar.gz/download
 - tar xzf SDL2_ttf-*.tar.gz
 - tar xzf SDL2_image-*.tar.gz