DW Energy may be wrong?

In the file ```https://github.com/noegroup/bgflow/blob/main/bgflow/distribution/energy/multi_double_well_potential.py```
Is there a missing linear term?
The energy may be supposed to be
```energies = self._a * dists ** 4 + self._b * dists ** 2 + self._c * dists```
Instead of 
```energies = self._a * dists ** 4 + self._b * dists ** 2 + self._c```
