fix typo in OpenType feature for superscripts

Author: John Daggett

css3-fonts/Fonts.html

@@ -3272,7 +3272,7 @@ <h3 id=font-variant-position-prop><span class=secno>6.4 </span>Subscript
   <p>The values ‘<code class=property>sub</code>’ and ‘<code
    class=property>super</code>’ imply the appropriate variant glyph is
    displayed when available in the font (OpenType features: <code>subs,
-   supr</code>). A value of ‘<a href="#normal2"><code
+   sups</code>). A value of ‘<a href="#normal2"><code
    class=property>normal</code></a>’ implies neither of these alternate
    glyphs are substituted.