making http calls proxy-aware

[edublancas]

corporate environments often have HTTP proxies; however, some of our calls are ignoring the proxy settings (often set via an environment variable).

to see the full context: #55

I'm assuming posthog is already taking care of it, but we still have two calls where we use HTTPSConnection that are most likely ignoring proxy settings

based on this, it looks like the requests library already takes care of this, so we can simply switch the calls to use requests (although we should verify that these assumptions are correct). Since the posthog package already has requests as a dependency, we are not really adding new dependencies, although we should explicitly put in our setup.py