Fix wording

Author: timhoffm

lib/matplotlib/contour.py

@@ -1490,8 +1490,8 @@ def _initialize_x_y(self, z):
     to automatically choose no more than *n+1* "nice" contour levels
     between minimum and maximum numeric values of *Z*.
 
-    If None (default), a reasonable default is chosen; for linear
-    scales, *n*=7 is the default.
+    If not given, a reasonable default is chosen; for linear scales,
+    *n*=7 is the default.
 
     If array-like, draw contour lines at the specified levels.
     The values must be in increasing order.