Update development dependencies to Dash 2.x

[akx]

About

I noticed that pip install -e . installed Dash 2.x, and then installing requirements as per CONTRIBUTING.md downgraded Dash to 1.x, which didn't quite seem right.

Description of changes

• remove the Python 2.x biopython dependency; the package isn't expected to run on Python 2
• bump Dash dependency to any 2.x version (2.0 was released in Sep 2021)

Pre-Merge checklist

• [x] The project was correctly built with npm run build:all.
• [x] If there was any conflict, it was solved correctly.
• [ ] All changes were documented in CHANGELOG.md.
• [ ] All tests on CircleCI have passed.
• [ ] All Percy visual changes have been approved.
• [ ] Two people have :dancer:'d the pull request. You can be one of these people if you are a Dash Cytoscape core contributor.