chore(git): ignore superset/app/ folder (#13767)
chore(git): ignore superset/app/ folder (#13767)

upload generate this folder in the form of /app/static/uploads
airbnb/caravel,zhouyao1994/incubator-superset,mistercrunch/panoramix,airbnb/caravel,apache/incubator-superset,zhouyao1994/incubator-superset,mistercrunch/panoramix,apache/incubator-superset,zhouyao1994/incubator-superset,airbnb/caravel,apache/incubator-superset,mistercrunch/panoramix,mistercrunch/panoramix,airbnb/caravel,apache/incubator-superset,apache/incubator-superset,zhouyao1994/incubator-superset,zhouyao1994/incubator-superset