tweak font-weight range to [1..1000]

The OpenType 1.8 spec defines the usWeightClass value as being between [1..1000]

Author: nattokirai

css-fonts-4/Overview.bs

@@ -96,7 +96,7 @@ rules defined in CSS3 Fonts.</p>
 
 <p>Expand the range of weights possible within the <code>font-weight</code>
 property and <code>font-weight</code> descriptor to include integer values within
-the range [1..999]. Define precisely how the font matching algorithm works
+the range [1..1000]. Define precisely how the font matching algorithm works
 when using weights in this range.</p>
 
 <p class="example">Example of using new font weights mixed with old ones</p>