FIX: sign is not defined

Use `np.sign` instead.

Author: tacaswell

lib/matplotlib/projections/polar.py

@@ -471,10 +471,10 @@ def get_rlabel_position(self):
             The theta position of the radius labels in degrees.
         """
         return self._r_label_position.to_values()[4]
-    
+
     def set_rlabel_position(self, value):
         """Updates the theta position of the radius labels.
-        
+
         Parameters
         ----------
         value : number
@@ -659,7 +659,7 @@ def drag_pan(self, button, key, x, y):
             dt0 = t - startt
             dt1 = startt - t
             if abs(dt1) < abs(dt0):
-                dt = abs(dt1) * sign(dt0) * -1.0
+                dt = abs(dt1) * np.sign(dt0) * -1.0
             else:
                 dt = dt0 * -1.0
             dt = (dt / np.pi) * 180.0