Move internal modules to “internal” folder.

.internal/hashHas.js

@@ -0,0 +1,20 @@
+import nativeCreate from './.internal/nativeCreate.js';
+
+/** Used to check objects for own properties. */
+const hasOwnProperty = Object.prototype.hasOwnProperty;
+
+/**
+ * Checks if a hash value for `key` exists.
+ *
+ * @private
+ * @name has
+ * @memberOf Hash
+ * @param {string} key The key of the entry to check.
+ * @returns {boolean} Returns `true` if an entry for `key` exists, else `false`.
+ */
+function hashHas(key) {
+  const data = this.__data__;
+  return nativeCreate ? (data[key] !== undefined) : hasOwnProperty.call(data, key);
+}
+
+export default hashHas;