circleci: brew uninstall python
circleci: brew uninstall python

This attempts to work around the error:

```
==> Pouring xz-5.2.4.sierra.bottle.tar.gz
🍺  /usr/local/Cellar/xz/5.2.4: 92 files, 1MB
Error: python is already installed from !
Please `brew uninstall python` first."
Exited with code 1
```

Signed-off-by: David Scott <63c9eb0ea83039690fefa11afe17873ba8278a56@docker.com>

djs55/vpnkit,djs55/vpnkit,djs55/vpnkit