update requirements.txt and Dockerfile for successful build

[JohnDoeAntler]

With higher version of virtualenv installed, attempting the installation of jsmin==2.2.1 yields error, therefore, updated to 3.0.1.

Once updated, in order to make manage.py runs properly, markupsafe and sqlalchemy version are also needed to be updated.

Once applied changes on requirements.txt, the Dockerfile with python image version of 3.5 could not be built successfully, therefore update the image version up to 3.8-alpine.