automation: create Python 3.5 variant of requirements.txt The automation environment is refusing to build with the previous file because some dependencies won't install on Python 3.5. I couldn't find an easy way to salvage the situation with a single requirements.txt file. So, I decided to introduce a variant for Python 3.5. As part of this, we update packages to latest versions. (I do question why we are still supporting Python 3.5...) Differential Revision: https://phab.mercurial-scm.org/D10690