fix: also support passed ES modules from css-loader in addition to CommonJS format (#47)

Author: foxxyz

Diff for: index.js

@@ -36,6 +36,8 @@ module.exports.pitch = function (remainingRequest) {
     '',
     '// load the styles',
     'var content = require(' + request + ');',
+    // get default export if list is an ES Module (CSS Loader v4+)
+    "if(content.__esModule) content = content.default;",
     // content list format is [id, css, media, sourceMap]
     "if(typeof content === 'string') content = [[module.id, content, '']];",
     'if(content.locals) module.exports = content.locals;'