Index: wp-content/themes/twentythirteen/css/blocks.css
===================================================================
--- wp-content/themes/twentythirteen/css/blocks.css	(revision 54300)
+++ wp-content/themes/twentythirteen/css/blocks.css	(working copy)
@@ -287,7 +287,6 @@
 }
 
 .wp-block-table td {
-	border: 0;
 	border-top: 1px solid #ededed;
 }