Running Cachet behind a proxy without Internet access

Hello,

I am running Cachet behind a proxy without Internet access.
The classic way is to pass `HTTP_PROXY` and `HTTPS_PROXY` environment variables.

However, those variables are not passed to the PHP FPM process, so they are not taken into account.

I've managed to hotfix it like this for the moment:

```Dockerfile
FROM cachethq/docker:2.3.15
RUN set -e; \
# HOTFIX: pass HTTP_PROXY and HTTPS_PROXY to FPM
echo '[www]' > /etc/php7/php-fpm.d/proxy-hotfix.conf; \
echo 'env[HTTP_PROXY] = $HTTP_PROXY' >> /etc/php7/php-fpm.d/proxy-hotfix.conf; \
echo 'env[HTTPS_PROXY] = $HTTPS_PROXY' >> /etc/php7/php-fpm.d/proxy-hotfix.conf
```

Is it possible to fix it correctly?

PS: if I don't do this, Cachet takes 30sec to log-in to the dashboard, because it performs requests to Github to find latest version number.

Thank you,