Bump to v4.0.0.

internal/cloneSet.js

@@ -0,0 +1,17 @@
+import addSetEntry from './addSetEntry';
+import arrayReduce from './arrayReduce';
+import setToArray from './setToArray';
+
+/**
+ * Creates a clone of `set`.
+ *
+ * @private
+ * @param {Object} set The set to clone.
+ * @returns {Object} Returns the cloned set.
+ */
+function cloneSet(set) {
+  var Ctor = set.constructor;
+  return arrayReduce(setToArray(set), addSetEntry, new Ctor);
+}
+
+export default cloneSet;