Update documentation index sidebar for 3.6.0 release.

diff --cc Doc/tools/templates/indexsidebar.html
index 5067c6e786debe3b9ac55dc1bbe1db5a43718651,413c0a7699cbe83563121f3592d079c3e5a35d25..72a4d7ae996abe569a09ce82c398af22cef8a030
--- 1/Doc/tools/templates/indexsidebar.html
--- 2/Doc/tools/templates/indexsidebar.html
+++ b/Doc/tools/templates/indexsidebar.html
@@@ -4,7 -4,7 +4,7 @@@
  <ul>
    <li><a href="https://docs.python.org/2.7/">{% trans %}Python 2.7 (stable){% endtrans %}</a></li>
    <li><a href="https://docs.python.org/3.5/">{% trans %}Python 3.5 (stable){% endtrans %}</a></li>
-   <li><a href="https://docs.python.org/3.6/">{% trans %}Python 3.6 (pre-release){% endtrans %}</a></li>
 -  <li><a href="https://docs.python.org/3.7/">{% trans %}Python 3.7 (in development){% endtrans %}</a></li>
++  <li><a href="https://docs.python.org/3.6/">{% trans %}Python 3.6 (stable){% endtrans %}</a></li>
    <li><a href="https://www.python.org/doc/versions/">{% trans %}Old versions{% endtrans %}</a></li>
  </ul>