Change documentation of legend to reflect default upper-right

The documentation stated that the default legend position was 0, corresponding
to "best". This does not match the behavior of the current code, which
uses as default the rcParam value "legend.loc", which at time of writing
defaults to "upper-right".

Author: ndevenish

lib/matplotlib/axes/_axes.py

@@ -288,7 +288,7 @@ def legend(self, *args, **kwargs):
 
         Parameters
         ----------
-        loc : int or string or pair of floats, default: 0
+        loc : int or string or pair of floats, default: 'upper right'
             The location of the legend. Possible codes are:
 
                 ===============   =============