bugfix: Undo Change to VecMag (#52)

Introduced due to a mistake made by git in merging excited state nodes and examples

hippynn/layers/physics.py

@@ -247,7 +247,7 @@ def forward(self, features, species):
 
 class VecMag(torch.nn.Module):
     def forward(self, vector_feature):
-        return torch.norm(vector_feature, dim=1).unsqueeze(1)
+        return torch.norm(vector_feature, dim=1)
 
 
 class CombineEnergy(torch.nn.Module):