Merge pull request #37 from Osukaru/master

Added missing error class imports

Author: rtheunissen

src/Queue.php

@@ -1,6 +1,7 @@
 <?php
 namespace Ds;
 
+use Error;
 use OutOfBoundsException;
 
 /**

src/Stack.php

@@ -1,6 +1,7 @@
 <?php
 namespace Ds;
 
+use Error;
 use OutOfBoundsException;
 
 /**