update Piwik to version 2.16 (fixes #91)

www/analytics/vendor/piwik/device-detector/Cache/Cache.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * Device Detector - The Universal Device Detection library for parsing User Agents
+ *
+ * @link http://piwik.org
+ * @license http://www.gnu.org/licenses/lgpl.html LGPL v3 or later
+ */
+
+namespace DeviceDetector\Cache;
+
+interface Cache
+{
+    public function fetch($id);
+
+    public function contains($id);
+
+    public function save($id, $data, $lifeTime = 0);
+
+    public function delete($id);
+
+    public function flushAll();
+}