Fix typo.

Author: mdboom

Diff for: lib/matplotlib/markers.py

@@ -281,7 +281,7 @@ def _set_circle(self, reduction = 1.0):
     def _set_pixel(self):
         self._path = Path.unit_rectangle()
         self._transform = Affine2D().translate(-0.49999, -0.50001)
-        self._snap_threshold = False
+        self._snap_threshold = None
 
     def _set_point(self):
         self._set_circle(reduction = self._point_size_reduction)