`floatfmt` doesn't work when `tablefmt="pretty"`

Reproduced with `tabulate==0.8.7`

```python
import tabulate


table = tabulate.tabulate(
    [
        [1.10000001],
    ],
    tablefmt="pretty",
    floatfmt=".3f",
)

print(table)
```

yields

```
+------------+
| 1.10000001 |
+------------+
```

instead of

```
+-------+
| 1.100 |
+-------+
```