chore: remove gunicorn and gevent from minimum requirements

It is now up to the user to install these (or other) for production deployment.
More info: https://flask.palletsprojects.com/en/1.1.x/tutorial/deploy/#run-with-a-production-server

Dockerfile

@@ -1,8 +1,9 @@
-FROM python:3.7
+FROM python:3.8-slim
 
 WORKDIR /app
 COPY requirements.txt /app/
 RUN pip install --no-cache-dir -q -r requirements.txt
+RUN pip install --no-cache-dir -q gunicorn gevent
 COPY . /app
 
 EXPOSE 5000