migrate to "export default"

also, set no-use-before-define in linter

src/underscore.js

@@ -1,12 +1,5 @@
 import assert from 'node:assert';
 
-export {
-    pick,
-    omit,
-    intersection,
-    isEqual,
-    difference
-};
 
 // IMPORTANT: this file is required from the migration logic. avoid requires
 
@@ -54,3 +47,11 @@ function difference(array, values) {
     const valueSet = new Set(values);
     return array.filter(item => !valueSet.has(item));
 }
+
+export default {
+    pick,
+    omit,
+    intersection,
+    isEqual,
+    difference
+};