[css-writing-mode] Fix pluralization in Applies-to

Author: fantasai

css-writing-modes-3/Overview.bs

@@ -789,7 +789,7 @@ Block Flow Direction: the 'writing-mode' property</h3>
   Name: writing-mode
   Value: horizontal-tb | vertical-rl | vertical-lr
   Initial: horizontal-tb
-  Applies to: All elements except table row groups, table column groups, table rows, table columns, ruby base container, ruby annotation container
+  Applies to: All elements except table row groups, table column groups, table rows, table columns, ruby base containers, ruby annotation containers
   Inherited: yes
   Percentages: n/a
   Computed value: specified value

css-writing-modes-4/Overview.bs

@@ -856,7 +856,7 @@ Block Flow Direction: the 'writing-mode' property</h3>
   Name: writing-mode
   Value: horizontal-tb | vertical-rl | vertical-lr | sideways-rl | sideways-lr
   Initial: horizontal-tb
-  Applies to: All elements except table row groups, table column groups, table rows, table columns, ruby base container, ruby annotation container
+  Applies to: All elements except table row groups, table column groups, table rows, table columns, ruby base containers, ruby annotation containers
   Inherited: yes
   Percentages: n/a
   Computed value: specified value