shexeval invocation doesn't work

If you
```bash
pipenv install pyshex
pipenv run shexeval
```
you get:
```
Traceback (most recent call last):
  File "/Users/solbrig/.local/share/virtualenvs/zzf-MnAwF90I/bin/shexeval", line 5, in <module>
    from PyShEx.shex_evaluator import evaluate_cli
ModuleNotFoundError: No module named 'PyShEx'
```

This is because the package name is `pyshex`, not `PyShEx`