correction for Linthub (code style)

Author: danielhkl

test/test_image_plot.py

@@ -14,6 +14,7 @@
 # the picture 'lena.png' with origin='lower' is flipped upside-down.
 # So it has to be upside-down in the pdf-file as well.
 
+
 # test for monochrome picture
 def plot1():
 
@@ -57,4 +58,4 @@ def plot2():
     )
 def test(plot, phash):
     helpers.assert_phash(plot(), phash)
-    return
+    return