Avoid deprecated pretty_hours() function

tailbone/grids/core.py

@@ -32,7 +32,7 @@ import sqlalchemy as sa
 from sqlalchemy import orm
 
 from rattail.db.types import GPCType
-from rattail.util import prettify, pretty_boolean, pretty_quantity, pretty_hours
+from rattail.util import prettify, pretty_boolean, pretty_quantity
 from rattail.time import localtime
 
 import webhelpers2_grid
@@ -541,7 +541,8 @@ class Grid(object):
         value = self.obtain_value(obj, field)
         if value is None:
             return ""
-        return pretty_hours(hours=value)
+        app = self.request.rattail_config.get_app()
+        return app.render_duration(hours=value)
 
     def set_url(self, url):
         self.url = url