Update for ORM changes (Django 1.10+ compatibility)

Closes #1, #2

Author: acdha

README.rst

@@ -13,7 +13,7 @@ django-tabular-export
     :target: http://django-tabular-export.readthedocs.org/en/latest/?badge=latest
     :alt: Documentation Status
 
-Simple spreadsheet exports from Django
+Simple spreadsheet exports from Django 1.8+
 
 Documentation
 -------------

tabular_export/core.py

@@ -45,11 +45,7 @@ def get_field_names_from_queryset(qs):
     field_names = []
     field_names.extend(i.target.name for i in v_qs.query.select)
     field_names.extend(v_qs.query.extra_select.keys())
-    try:
-        # for django 1.10 and up (works starting in 1.8)
-        field_names.extend(v_qs.query.annotation_select.keys())
-    except AttributeError:
-        field_names.extend(v_qs.query.aggregate_select.keys())
+    field_names.extend(v_qs.query.annotation_select.keys())
 
     return field_names