STYLE enable B005 check in flake8-bugbear
From https://github.com/pandas-dev/pandas/pull/40570#issuecomment-811515884

> B005 would also be great

I agree, `strip` / `rstrip` / `lstrip` are common sources of confusion https://docs.python.org/3/library/stdtypes.html#str.lstrip , e.g.
```python
>>> 'Arthur: three!'.lstrip('Arthur: ')
'ee!'
```
Thanks @twoertwein for reviewing!