plakativ.py: format with black

plakativ.py

@@ -2105,13 +2105,16 @@ def parse_pagesize_rectarg(string):
 
 def main():
     if len(sys.argv) == 1 and platform.system() != "Windows":
-        print("""
+        print(
+            """
 You called plakativ without arguments. At least one of the options --size,
 --factor or --maxpages is required for running plakativ on the command line.
 But maybe you meant to run the plakativ GUI instead? On platforms other than
 Windows, the default is to run the command line interface. To run the graphical
 user interface, run plakativ with the --gui option instead.
-""", file=sys.stderr)
+""",
+            file=sys.stderr,
+        )
 
     rendered_papersizes = ""
     for k, v in sorted(papersizes.items()):