revert to nth-child styling for vector clock table

Author: mycognosist

css/guide.css

@@ -320,11 +320,11 @@ table.clock-values tr {
  border-bottom: solid thin #fff;
 }
 
-table.clock-values thead tr:first-child {
+table.clock-values thead tr:nth-child(1) {
  background-color: #ca82c9;
 }
 
-table.clock-values thead tr:second-child {
+table.clock-values thead tr:nth-child(2) {
  background-color: #f29bce;
 }