Replace naive datetime with timezone aware.

Also clean-up unused imports.

program/serializers.py

-# -*- coding: utf-8 -*-
-
+from django.contrib.auth.models import User
 from django.core.exceptions import ObjectDoesNotExist
-from django.contrib.auth.models import User, Group
-from rest_framework import serializers, status
-from rest_framework.response import Response
-from program.models import Show, Schedule, TimeSlot, Category, FundingCategory, Host, Language, Topic, MusicFocus, Note, Type, Language, RRule
+from django.utils import timezone
+from rest_framework import serializers
+
 from profile.models import Profile
 from profile.serializers import ProfileSerializer
-from datetime import datetime
-
+from program.models import Show, Schedule, TimeSlot, Category, FundingCategory, Host, Topic, MusicFocus, Note, Type, Language, \
+    RRule
 from pv.settings import THUMBNAIL_SIZES
 
+
 class UserSerializer(serializers.ModelSerializer):
     # Add profile fields to JSON
     profile = ProfileSerializer()
@@ -28,7 +27,7 @@ class UserSerializer(serializers.ModelSerializer):
         profile_data = validated_data.pop('profile')
 
         user = super(UserSerializer, self).create(validated_data)
-        user.date_joined = datetime.today()
+        user.date_joined = timezone.now()
         user.set_password(validated_data['password'])
         user.save()