[css-text-3] Fix contradiction in propdef table for computed value of word-spacing. w3c#3515

Author: fantasai

css-text-3/Overview.bs

@@ -3296,7 +3296,7 @@ Word Spacing: the 'word-spacing' property</h3>
   Applies to: <a>inline boxes</a>
   Inherited: yes
   Percentages: N/A
-  Computed value: the keyword ''word-spacing/normal'' or an absolute length
+  Computed value: an absolute length
   Animation type: by computed value type
   Canonical order: n/a
   </pre>