[css-pseudo-4] Compatibilit{iy -> y}

Author: Fayti1703

css-pseudo-4/Overview.bs

@@ -951,7 +951,7 @@ Additions to the CSS Object Model</h2>
   and <a href="https://github.com/w3c/csswg-drafts/issues/3603">Issue 3603</a>.
 
 <h2 id="css2-compat">
-Compatibilitiy Syntax</h2>
+Compatibility Syntax</h2>
 
   <p>For compatibility with existing style sheets written against CSS Level 2 [[CSS2]],
   user agents must also accept the previous one-colon notation