Modularize master branch.

_customOmitClone.js

@@ -0,0 +1,16 @@
+import isPlainObject from './isPlainObject.js';
+
+/**
+ * Used by `_.omit` to customize its `_.cloneDeep` use to only clone plain
+ * objects.
+ *
+ * @private
+ * @param {*} value The value to inspect.
+ * @param {string} key The key of the property to inspect.
+ * @returns {*} Returns the uncloned value or `undefined` to defer cloning to `_.cloneDeep`.
+ */
+function customOmitClone(value, key) {
+  return (key !== undefined && isPlainObject(value)) ? undefined : value;
+}
+
+export default customOmitClone;