use postgres json field

pandora/changelog/migrations/0002_jsonfield.py

@@ -0,0 +1,22 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.9.4 on 2018-06-19 17:23
+from __future__ import unicode_literals
+
+import django.contrib.postgres.fields.jsonb
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('changelog', '0001_initial'),
+    ]
+
+    operations = [
+        migrations.RunSQL(
+            'ALTER TABLE "changelog_changelog" ALTER COLUMN "value" TYPE jsonb USING "value"::text::jsonb'
+        ),
+        migrations.RunSQL(
+            'ALTER TABLE "changelog_log" ALTER COLUMN "data" TYPE jsonb USING "data"::text::jsonb'
+        ),
+    ]