Error with Python3 runtime

## Prerequisites

* [x] I am running the latest version. (`up upgrade`)
* [x] I searched to see if the issue already exists.
* [x] I inspected the verbose debug output with the `-v, --verbose` flag.
* [ ] Are you an Up Pro subscriber?

## Description

Getting ``Unable to import module '_proxy': No module named '_proxy'`` in logs when deployed to staging/AWS.

## Steps to Reproduce

Using Python3.6 runtime and proxy override of "python3 app.py". Runs perfectly locally, but on deploy does not work and checking up logs gives ``Unable to import module '_proxy': No module named '_proxy'``

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