arrow package missing from setup.py

[igboyes]

Make sure all packages required for install are listed in install_requires.

    return get_distribution(dist).load_entry_point(group, name)
  File "/home/igboyes/.venv/ref/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2862, in load_entry_point
    return ep.load()
  File "/home/igboyes/.venv/ref/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2462, in load
    return self.resolve()
  File "/home/igboyes/.venv/ref/lib/python3.7/site-packages/pkg_resources/__init__.py", line 2468, in resolve
    module = __import__(self.module_name, fromlist=['__name__'], level=0)
  File "/home/igboyes/.venv/ref/lib/python3.7/site-packages/virtool_cli/run.py", line 2, in <module>
    import virtool_cli.build
  File "/home/igboyes/.venv/ref/lib/python3.7/site-packages/virtool_cli/build.py", line 3, in <module>
    import arrow
ModuleNotFoundError: No module named 'arrow'