Remove extraneous colon from heading for 'WAI-ARIA Roles, States, and Properties' (pull #3302)

Resolves issue #3300 by removing the trailing colon (:) character at the end of the heading for roles, states, and properties.

Author: mcking65

content/patterns/accordion/accordion-pattern.html

@@ -74,7 +74,7 @@ <h2>Keyboard Interaction</h2>
       </section>
 
       <section id="roles_states_properties">
-        <h2>WAI-ARIA Roles, States, and Properties:</h2>
+        <h2>WAI-ARIA Roles, States, and Properties</h2>
         <ul>
           <li>The title of each accordion header is contained in an element with role <a href="#button" class="role-reference">button</a>.</li>
           <li>