Bugfix : transverse wake potential

Fix dipole_moment due to switch to numpy arrays for Bunch.binning

tracking/wakepotential.py

@@ -141,9 +141,9 @@ class WakePotential(Element):
             Dipole moment of the bunch.
 
         """
-        dipole = np.zeros((self.n_bin,))
-        for i in range(self.n_bin):
-            dipole[i] = bunch[plane][self.sorted_index == self.bins[i]].sum()
+        dipole = np.zeros((self.n_bin - 1,))
+        for i in range(self.n_bin - 1):
+            dipole[i] = bunch[plane][self.sorted_index == i].sum()
         dipole = dipole/self.profile
         dipole[np.isnan(dipole)] = 0