Update sidebar.html

american US wording

Author: michal-at-travisci

_includes/sidebar.html

@@ -160,7 +160,7 @@ <h3>Travis CI Enterprise</h3>
   <section class="sidebar-notice">
     <p>This documentation site is Open Source.
       The <a href="https://github.com/travis-ci/docs-travis-ci-com">README in our Git repository</a> explains how to contribute.</p>
-    <p>Travis CI relies on Open Source <a href="/user/open_source_licence/">licensing information</a>.</p>
+    <p>Travis CI relies on Open Source <a href="/user/open_source_license/">licensing information</a>.</p>
   </section>
 
 </div><!-- /#sidebar -->