Switch to ESM format (#21)

Author: Joel Denning

package.json

@@ -45,7 +45,7 @@
     "single-spa-react": "^3.2.0",
     "webpack": "^5.15.0",
     "webpack-cli": "^4.3.1",
-    "webpack-config-single-spa-react": "^2.0.0",
+    "webpack-config-single-spa-react": "^5.0.2",
     "webpack-dev-server": "^4.0.0-beta.0",
     "webpack-merge": "^5.7.3"
   },