update python version to 3.7; uses root user in containers on production; update nginx version

compose/local/django/Dockerfile

-FROM python:3.6
+FROM python:3.7
 LABEL mantainer "Hacklab <contato@hacklab.com.br>"
 ENV PYTHONUNBUFFERED 1
 

compose/production/Dockerfile

-FROM python:3.6 as django
+FROM python:3.7 as django
 LABEL mantainer "Hacklab <contato@hacklab.com.br>"
 ENV PYTHONUNBUFFERED 1
 
-# Ensure that the the internal user and
-# group used by django have a known uid and gid
-RUN groupadd -r -g 999 django \
-    && useradd -r -u 999 -g django django
 
 # Requirements have to be pulled and installed here, otherwise caching won't work
 COPY ./requirements /requirements
@@ -15,32 +11,24 @@ RUN pip install --no-cache-dir -r /requirements/production.txt \
 COPY ./compose/production/django/gunicorn.sh /gunicorn.sh
 RUN sed -i 's/\r//' /gunicorn.sh
 RUN chmod +x /gunicorn.sh
-RUN chown django /gunicorn.sh
 
 COPY ./compose/production/django/entrypoint.sh /entrypoint.sh
 RUN sed -i 's/\r//' /entrypoint.sh
 RUN chmod +x /entrypoint.sh
-RUN chown django /entrypoint.sh
 
 COPY . /app
 
-RUN mkdir /app/staticfiles
-
 # env.example must be used during build to provide a valid environment
 RUN export $(cat /app/env.example | grep -v ^# | xargs) && \
     python /app/manage.py collectstatic --noinput
 
-RUN chown -R django /app
-
-USER django
-
 WORKDIR /app
 
 ENTRYPOINT ["/entrypoint.sh"]
 CMD ["/gunicorn.sh"]
 
 
-FROM nginx:1.13 as nginx
+FROM nginx:1.16 as nginx
 
 COPY ./compose/production/nginx/default.conf /etc/nginx/conf.d/default.conf
 COPY --from=django /app/staticfiles/static/ /usr/share/nginx/html/static/