Fix grammar error

Author: fantasai

css-2010/Overview.html

@@ -374,7 +374,7 @@ <h3 id=experimental><span class=secno>3.3. </span>Experimental
    Drafts. This avoids incompatibilities with future changes in the draft.
 
   <p class=note>For legacy reasons, certain experimental CSS properties do
-   not follow this prefixing convention. Three common examples are the
+   not follow this prefixing convention. Two common examples are the
    &lsquo;<code class=property>word-wrap</code>&rsquo; and &lsquo;<code
    class=property>text-overflow</code>&rsquo; properties, which were
    introduced unprefixed by Microsoft Internet Explorer prior to the

css-2010/Overview.src.html

@@ -251,7 +251,7 @@ <h3 id="experimental">Experimental Implementations</h3>
 </p>
 
 <p class="note">For legacy reasons, certain experimental CSS properties
-do not follow this prefixing convention. Three common examples are the
+do not follow this prefixing convention. Two common examples are the
 'word-wrap' and 'text-overflow' properties,
 which were introduced unprefixed by Microsoft Internet Explorer prior
 to the introduction of the vendor prefixing policy in CSS2.1 and were