[css-background] Add missed "internal" into "applies to" for <'border-image-width'> (w3c#1379)

Author: lahmatiy

css-backgrounds/Overview.html

@@ -3431,7 +3431,7 @@ <h3 id=the-border-image-width><span class=secno>6.3. </span>Drawing Areas:
     <tr>
      <th>Applies to:
 
-     <td>All elements, except table elements when ‘<code
+     <td>All elements, except internal table elements when ‘<code
       class=property>border-collapse</code>’ is ‘<code
       class=css>collapse</code>’
 

css-backgrounds/Overview.src.html

@@ -2464,7 +2464,7 @@ <h3 id="the-border-image-width">Drawing Areas: the 'border-image-width' property
     <td>1
   <tr>
     <th>Applies to:
-    <td>All elements, except table elements when 'border-collapse' is
+    <td>All elements, except internal table elements when 'border-collapse' is
     ''collapse''
   <tr>
     <th>Inherited: