fixing typo

Author: howcome

css-multicol/Overview.src.html

@@ -1103,7 +1103,7 @@ <h3>'column-rule'</h3>
 
 <div class=example>
 <p>If a tall image is moved to a column on the next page to find room
-for it, its natural column may be left empty. If so, the column is is
+for it, its natural column may be left empty. If so, the column is 
 still considered to have content for the purpose of deciding if the
 column rule should be drawn.
 </div>