Switch travisci to pre-whitelisted mysql-5.7.
Switch travisci to pre-whitelisted mysql-5.7.

TravisCI recently made changes where key_url isn't fetched unless
safelisting is disabled.

omkelderman/osu-web,kj415j45/osu-web,nanaya/osu-web,LiquidPL/osu-web,notbakaneko/osu-web,notbakaneko/osu-web,omkelderman/osu-web,ppy/osu-web,nanaya/osu-web,LiquidPL/osu-web,nanaya/osu-web,notbakaneko/osu-web,LiquidPL/osu-web,notbakaneko/osu-web,kj415j45/osu-web,ppy/osu-web,nekodex/osu-web,kj415j45/osu-web,omkelderman/osu-web,ppy/osu-web,kj415j45/osu-web,nekodex/osu-web,LiquidPL/osu-web,nanaya/osu-web,nekodex/osu-web,ppy/osu-web,omkelderman/osu-web,nekodex/osu-web,LiquidPL/osu-web,nanaya/osu-web,notbakaneko/osu-web,ppy/osu-web,nekodex/osu-web