Fix new pep8 issue in legend_demo5

Author: jenshnielsen

examples/pylab_examples/legend_demo5.py

@@ -41,7 +41,7 @@ def create_artists(self, legend, orig_handle,
                 lw = orig_handle.get_linewidths()[i]
             except IndexError:
                 lw = orig_handle.get_linewidths()[0]
-            if dashes[0] != None:
+            if dashes[0] is not None:
                 legline.set_dashes(dashes[1])
             legline.set_color(color)
             legline.set_transform(trans)