Merge pull request googleapis#168 from chixor/master

Replaced non existing variable $now with mktime().

Author: ianbarber

src/Google/Cache/File.php

@@ -48,7 +48,7 @@ public function get($key, $expiration = false)
 
     if ($expiration) {
       $mtime = filemtime($storageFile);
-      if (($now - $mtime) >= $expiration) {
+      if ((mktime() - $mtime) >= $expiration) {
         $this->delete($key);
         return false;
       }