pygrass: fix GridModule after renaming a method in https://trac.osgeo.org/grass/changeset/60491, see https://trac.osgeo.org/grass/ticket/2791 (merge from trunk, https://trac.osgeo.org/grass/changeset/66746)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@66747 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/python/pygrass/gis/__init__.py

@@ -392,7 +392,7 @@ class VisibleMapset(object):
             if lines:
                 return [l.strip() for l in lines]
         lns = ['PERMANENT', ]
-        self.write(lns)
+        self._write(lns)
         return lns
 
     def _write(self, mapsets):