Bump to v4.0.0.

internal/mapClear.js

@@ -0,0 +1,15 @@
+var Hash = require('./Hash'),
+    Map = require('./Map');
+
+/**
+ * Removes all key-value entries from the map.
+ *
+ * @private
+ * @name clear
+ * @memberOf MapCache
+ */
+function mapClear() {
+  this.__data__ = { 'hash': new Hash, 'map': Map ? new Map : [], 'string': new Hash };
+}
+
+module.exports = mapClear;