Merge pull request matplotlib#4080 from efiring/no_show_in_test

test_axes: remove extraneous "show()"

Author: efiring

lib/matplotlib/tests/test_axes.py

@@ -3503,7 +3503,6 @@ def test_color_None():
     # issue 3855
     fig, ax = plt.subplots()
     ax.plot([1,2], [1,2], color=None)
-    plt.show()
 
 @cleanup
 def test_numerical_hist_label():