fix: Import of join_kwargs_in_sequence in FFD example (#156)

Closes #152.

Author: aschuh-hf

examples/ffd/pairwise.py

@@ -10,7 +10,7 @@
 
 from deepali.core import Axes, Device, Grid, PathStr
 from deepali.core import functional as U
-from deepali.core import join_kwargs_in_sequence
+from deepali.core.config import join_kwargs_in_sequence
 from deepali.data import FlowField, Image
 from deepali.losses import RegistrationResult, new_loss
 from deepali.spatial import DisplacementFieldTransform