Update to use interface instead of concreate class

Author: Westin Shafer

FilesystemCachePool.php

@@ -16,15 +16,15 @@
 use Cache\Adapter\Common\PhpCacheItem;
 use League\Flysystem\FileExistsException;
 use League\Flysystem\FileNotFoundException;
-use League\Flysystem\Filesystem;
+use League\Flysystem\FilesystemInterface;
 
 /**
  * @author Tobias Nyholm <[email protected]>
  */
 class FilesystemCachePool extends AbstractCachePool
 {
     /**
-     * @type Filesystem
+     * @type FilesystemInterface
      */
     private $filesystem;
 
@@ -36,10 +36,10 @@ class FilesystemCachePool extends AbstractCachePool
     private $folder;
 
     /**
-     * @param Filesystem $filesystem
+     * @param FilesystemInterface $filesystem
      * @param string     $folder
      */
-    public function __construct(Filesystem $filesystem, $folder = 'cache')
+    public function __construct(FilesystemInterface $filesystem, $folder = 'cache')
     {
         $this->folder = $folder;