Raspbian label gets hidden by icon

When using a label with `Raspbian`, the label gets hidden. Using a height attr of 2.2 works, but this should probably be handled in the buffer logic. This probably happens for other taller icons also, but I have not checked.

```
from diagrams.generic.os import Raspbian

with Diagram():
    Raspbian("label")
    Raspbian("label", height="2.2")
```