travisCI: add sdl2_mixer from mazmazz's srb2 tap

.travis.yml

@@ -250,11 +250,10 @@ addons:
     - libgme-dev
     - p7zip-full
   homebrew:
+    taps:
+    - mazmazz/srb2
     packages:
-    - libmodplug
-    - liboog
-    - libvorbis
-    - sdl2
+    - mazmazz/srb2/sdl2_mixer
     - game-music-emu
     - p7zip
     - cmake
@@ -271,7 +270,6 @@ before_script:
   - cmake .. -DCMAKE_BUILD_TYPE=Release
 
 before_install:
-  - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then brew install sdl2_mixer; fi
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then curl -O -L https://www.libsdl.org/release/SDL2-2.0.6.dmg; hdiutil attach SDL2-2.0.6.dmg; sudo cp -a /Volumes/SDL2/SDL2.framework /Library/Frameworks/; fi
   - if [[ "$TRAVIS_OS_NAME" == "osx" ]]; then curl -O -L https://www.libsdl.org/projects/SDL_mixer/release/SDL2_mixer-2.0.1.dmg; hdiutil attach SDL2_mixer-2.0.1.dmg; sudo cp -a /Volumes/SDL2_mixer/SDL2_mixer.framework /Library/Frameworks/; fi
   - mkdir -p $HOME/srb2_cache