[webpack] fix copying images when running dev server (#9250)
[webpack] fix copying images when running dev server (#9250)


zhouyao1994/incubator-superset,airbnb/superset,mistercrunch/panoramix,mistercrunch/panoramix,apache/incubator-superset,airbnb/caravel,airbnb/superset,apache/incubator-superset,apache/incubator-superset,airbnb/superset,zhouyao1994/incubator-superset,mistercrunch/panoramix,airbnb/superset,mistercrunch/panoramix,airbnb/caravel,zhouyao1994/incubator-superset,apache/incubator-superset,apache/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset,airbnb/caravel,zhouyao1994/incubator-superset