Fix link to Rambler

It was counted as relative one.

docs/powered_by.rst

@@ -30,7 +30,7 @@ make a Pull Request!
   bikes location.
 * `Wargaming: World of Tanks <https://worldoftanks.ru/>`_
 * `Yandex <https://yandex.ru>`_
-* `Rambler <rambler.ru>`_
+* `Rambler <https://rambler.ru>`_
 * `Escargot <https://escargot.log1p.xyz>`_ - Chat server
 * `Prom.ua <https://prom.ua/>`_ - Online trading platform
 * `globo.com <https://www.globo.com/>`_ - (some parts) Brazilian largest media portal