FIX: docker-compose was failing with SSL error (#474)
FIX: docker-compose was failing with SSL error (#474)

Using the previous base image, tiangolo/uwsgi-nginx-flask, gave
error with server certificate verification.
Refer https://github.com/tiangolo/uwsgi-nginx-flask-docker/issues/181 for more details.

Also, switched base image from python3.8 to python3.6 as psycopg2 as error on building
on python3.8.
Refer https://github.com/psycopg/psycopg2/issues/858 for more details.

Closes #473
HTTP-APIs/hydrus