Speed up macOS Travis CI builds
Speed up macOS Travis CI builds

Updating Homebrew takes more than 5 minutes. Upgrading other
things that depend on FreeType takes more than 6 minutes.
Together, that's 11+ minutes of build time gone to waste.

It seems Homebrew in the current default osx image has
all the dependencies we need without needing to update.

astiob/libass,ShiftMediaProject/libass,ShiftMediaProject/libass,libass/libass,Akemi/libass,libass/libass,xbmc/libass,MrSmile/libass,Akemi/libass,MrSmile/libass,astiob/libass,Akemi/libass,xbmc/libass