Minor bug in the error message OnionSmoothInsight.

In `dump_colored_trj`, it should be replaced `self.labels.shape[0]` with `self.labels.shape[1]`.
```python
if self.labels.shape != (n_atoms, n_frames):
    msg = (
        f"Shape mismatch: Trj should have {self.labels.shape[0]} "
        f"atoms, {self.labels.shape[0]} frames, but has {n_atoms} "
        f"atoms, {n_frames} frames."
    )
    logger.log(msg)
    raise ValueError(msg)
```