[css-writing-modes] Fix 'maybe' refs for float/clear

Author: Koji Ishii

css-writing-modes/Overview.bs

@@ -23,6 +23,10 @@ Ignored Terms: glyph orientation, *-left, *-right, *-top, *-bottom, block contai
 Link Defaults: css21 (property) display/min-height/max-height/min-width/max-width/clip/left/right/bottom/top, css-text-3 (property) letter-spacing, css-text-decor-3 (property) text-decoration, svg2 (property) glyph-orientation-vertical/glyph-orientation-horizontal
 Use <i> Autolinks: yes
 </pre>
+<pre class=link-defaults>
+spec:css21; type:property; text:float
+spec:css21; type:property; text:clear
+</pre>
 
 <style>
 object { vertical-align: middle; }