comparators/directory.py: fix whitespace for black 21.12

Sergei Trofimovichrequested to merge
trofi/diffoscope:fix-for-black into master

On black-21.12 test fails as:

--- diffoscope/comparators/directory.py     2022-01-26 11:54:10.953755 +0000
+++ diffoscope/comparators/directory.py     2022-01-26 11:54:18.335859 +0000
@@ -46,11 +46,10 @@
                 "%Y-%m-%d %H:%M:%S",
                 "-f",
                 "%Sp %l %Su %Sg %z %Sm %k %b %#Xf",
                 self.path,
             ]
-
 else:
     class Stat(Command):

The change drops extra whitespace.

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