I’ve reviewed the script and I don’t think the issue is your python3 version, but pip3 is broken on your system somehow.
It seems I also misremembered the issue and the opposite is true, that is it’s likely your version of the requests module is too new, breaking compatibility with pip 1.5.6 (what ships with Raspbian).
I would have to guess that that came about through install of the requests module using pip3 as some point.
… you can check the result of my ‘detective work’ in the following topic:
http://forums.pimoroni.com/t/issue-installing-blinkt/3207
I would have to stick to my non-commital stance expressed there and probably advise that you start fresh by reimaging Raspbian and don’t permorm a dist-upgrade nor run any commands that pip install requests
… none of our one-line installers would do that, so running curl -sS https://get.pimoroni.com/explorerhat | bash should work.