documentation: fix grammar

Author: thomastrapp

jekyll/documentation.html

@@ -446,7 +446,7 @@ <h3>:attribute-count(&lt;amount&gt;)</h3>
     </div>
     <div class="column">
       <h3>:not(&lt;:trait&gt;)</h3>
-      <p>Select elements who do not match certain traits.</p>
+      <p>Select elements that don't match certain traits.</p>
     </div>
     <div class="column">
       <pre class="ace-static-hl"><code>{%include nt-not.hext%}</code></pre>