A typo in `setup.py`

In `setup.py` there should be a comma after `"anndata>=0.7.5"`, otherwise `pip` will ignore the `anndata` and `scikit-learn` dependencies.

```python
install_requires = [
    "numpy>=1.19.5",
    "pandas>=1.2.1",
    "scipy >=1.4.1",
    "anndata>=0.7.5"
    "scikit-learn>=0.24.2",
    "matplotlib",
    "seaborn>=0.11.1",
    "statsmodels>=0.12.2"
]
```