snscrape: fix startup

This fixes:

Traceback (most recent call last):
  File "/nix/store/607z14x0spsz1lsh0fg9cbyc9lr038mi-python3.7-snscrape-0.3.0/bin/.snscrape-wrapped", line 11, in <module>
    sys.exit(main())
  File "/nix/store/607z14x0spsz1lsh0fg9cbyc9lr038mi-python3.7-snscrape-0.3.0/lib/python3.7/site-packages/snscrape/cli.py", line 218, in main
    args = parse_args()
  File "/nix/store/607z14x0spsz1lsh0fg9cbyc9lr038mi-python3.7-snscrape-0.3.0/lib/python3.7/site-packages/snscrape/cli.py", line 154, in parse_args
    import snscrape.version
  File "/nix/store/607z14x0spsz1lsh0fg9cbyc9lr038mi-python3.7-snscrape-0.3.0/lib/python3.7/site-packages/snscrape/version.py", line 1, in <module>
    import pkg_resources
ModuleNotFoundError: No module named 'pkg_resources'

Related: https://github.com/NixOS/nixpkgs/pull/68314