backports-datetime-fromisoformat fails on -slim and alpine containers

[dhodun]

Not sure if there's really an alternative for this library (backports-datetime-fromisoformat), but just passing along we weren't able to do a simple 'pip install fireo' on pyton:3.6-slim, python:3.7-slim, and alpine base Docker containers. gcc was required to get it working, so we added in docker. (This is somewhat common when using slim containers).

# needed for backports-datetime-fromisoformat in fireo
RUN apt-get update
RUN apt-get -y install gcc

COPY requirements.txt .

RUN pip install fireo==1.4.1

[AxeemHaider]

backports-datetime-fromisoformat is not longer needed