fix broken link in footer (#947)

sphinx_rtd_theme/footer.html

@@ -46,12 +46,12 @@
   </div>
 
   {%- if show_sphinx %}
-    {% set sphinx_web = '<a href="http://sphinx-doc.org/">Sphinx</a>' %}
+    {% set sphinx_web = '<a href="https://www.sphinx-doc.org/">Sphinx</a>' %}
     {% set readthedocs_web = '<a href="https://readthedocs.org">Read the Docs</a>'  %}
     {# Translators: the variable "sphinx_web" is a link to the Sphinx project documentation with the text "Sphinx" #}
     {% trans sphinx_web=sphinx_web, readthedocs_web=readthedocs_web %}Built with {{ sphinx_web }} using a{% endtrans %}
     {# Translators: "theme" refers to a theme for Sphinx, which alters the appearance of the generated documenation #}
-    <a href="https://github.com/rtfd/sphinx_rtd_theme">{% trans %}theme{% endtrans %}</a>
+    <a href="https://github.com/readthedocs/sphinx_rtd_theme">{% trans %}theme{% endtrans %}</a>
     {# Translators: this is always used as "provided by Read the Docs", and should not imply Read the Docs is an author of the generated documentation. #}
     {% trans %}provided by {{ readthedocs_web }}{% endtrans %}.
   {%- endif %}