Fix outdated links

Update doc links according to OpenStack document migration.
Use https instead of http for docs links.
Closes-Bug:#1717171

Change-Id: I97ea62e22d8ae0913562fdd51226e1464416a66d

doc/source/contributing.rst

@@ -5,13 +5,13 @@ Contributing to: zaqar-specs
 If you would like to contribute to the development of OpenStack,
 you must follow the steps in this page:
 
-   http://docs.openstack.org/infra/manual/developers.html
+   https://docs.openstack.org/infra/manual/developers.html
 
 Once those steps have been completed, changes to OpenStack
 should be submitted for review via the Gerrit tool, following
 the workflow documented at:
 
-   http://docs.openstack.org/infra/manual/developers.html#development-workflow
+   https://docs.openstack.org/infra/manual/developers.html#development-workflow
 
 Pull requests submitted through GitHub will be ignored.