Pandas FutureWarning: Series.__getitem__ deprecation warning

In `higlass-python`, I'm getting an error with bigwig tracks:

```py
import higlass as hg

ts = hg.bigwig("/Users/manzt/Downloads/data.bw")
hg.view(ts.track().opts(barFillColor="red"))
```

```
clodius/tiles/utils.py:275: FutureWarning: Series.__getitem__ treating keys as positions is deprecated.
In a future version, integer keys will always be treated as labels (consistent with DataFrame behavior).
To access a value by position, use `ser.iloc[pos]`
yield cid, start, chromsizes[cid]
```

warning is referencing this line:

https://github.com/higlass/clodius/blob/de67e9df2cd296d3681dcf438c0895638de672e4/clodius/tiles/utils.py#L275