Fix string comparison

Author: timhoffm

lib/matplotlib/backends/qt_editor/figureoptions.py

@@ -217,7 +217,7 @@ def apply_callback(data):
             rgba = mcolors.to_rgba(color)
             line.set_alpha(None)
             line.set_color(rgba)
-            if marker is not 'none':
+            if marker != 'none':
                 line.set_marker(marker)
                 line.set_markersize(markersize)
                 line.set_markerfacecolor(markerfacecolor)