[css-writing-modes-3] Fix bikeshed error

Author: kojiishi

css-writing-modes-3/Overview.bs

@@ -2015,7 +2015,7 @@ Available Space in Orthogonal Flows</h4>
     and <i>inline axis</i> computations cannot be resolved.
     In these cases, the initial containing block's size is used
     as a <i>fallback</i> variable in place of the <i>available inline space</i>
-    for calculations that require a definite <i>available inline size</i>.
+    for calculations that require a definite <i>available inline space</i>.
 
   <p>See [[!CSS3-SIZING]] for further details on CSS sizing terminology and concepts.