adapt.css: fix diff border colors

adapt.css

@@ -161,6 +161,12 @@ h2.wikiaction { margin:0px }
 }
 
 /* Diff View */
+.diffadd {
+  border-color: #afa !important;
+}
+.diffdel {
+  border-color: #faa !important;
+}
 .diffmarkup del {
   background-color: #fdd !important;
 }