Unexpected skimage==0.0

First, thanks for the great tool!

I have

```py
from skimage.util import random_noise
from skimage import morphology
```

in my code.

When I use `pipreqs` to generate requirements.txt, it genertates
```
scikit_image==0.14.2
skimage==0.0
```

`scikit_image==0.14.2` is actually correct, while `skimage==0.0` is not necessary I think.