[pre-commit.ci] auto fixes from pre-commit.com hooks

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imlib/cells/cells.py

@@ -2,6 +2,7 @@
 Based on https://github.com/SainsburyWellcomeCentre/niftynet_cell_count by
 Christian Niedworok (https://github.com/cniedwor).
 """
+
 import os
 import re
 import math