Merge pull request matplotlib#932 from mdboom/fix_pcolor_edge_default

Fix pcolormesh edgecolors default

Author: efiring

lib/matplotlib/axes.py

@@ -7202,6 +7202,7 @@ def pcolormesh(self, *args, **kwargs):
         vmax = kwargs.pop('vmax', None)
         shading = kwargs.pop('shading', 'flat').lower()
         antialiased = kwargs.pop('antialiased', False)
+        kwargs.setdefault('edgecolors', 'None')
 
         X, Y, C = self._pcolorargs('pcolormesh', *args)
         Ny, Nx = X.shape