fix:css-module-compatible

[YanZiSen]

add compatible for css-loader>4.x and css-modules;

this situation css-loader transformed module will export.default;

this solution add a option getCss to get the transformed module;

useage:

{
  loader: "isomorphic-style-loader",
  options: {
    getCss: (css) => {
      return css.default;
    },
  },
},