Accessibility changes to headings (transitions.html)

docs/_includes/js/transitions.html

 <div class="bs-docs-section">
   <h1 id="transitions" class="page-header">Transitions <small>transition.js</small></h1>
 
-  <h3>About transitions</h3>
+  <h2>About transitions</h2>
   <p>For simple transition effects, include <code>transition.js</code> once alongside the other JS files. If you're using the compiled (or minified) <code>bootstrap.js</code>, there is no need to include this&mdash;it's already there.</p>
-  <h3>What's inside</h3>
+  <h2>What's inside</h2>
   <p>Transition.js is a basic helper for <code>transitionEnd</code> events as well as a CSS transition emulator. It's used by the other plugins to check for CSS transition support and to catch hanging transitions.</p>
 </div>