Fix task model updated_date field: auto_now = True (#2233)

* Fix task model updated_date field: auto_now = True

* update migrations file

cvat/apps/engine/migrations/0031_auto_20201011_0220.py

@@ -0,0 +1,18 @@
+# Generated by Django 3.1.1 on 2020-10-11 02:20
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('engine', '0030_auto_20200914_1331'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='task',
+            name='updated_date',
+            field=models.DateTimeField(auto_now=True),
+        ),
+    ]

cvat/apps/engine/models.py

@@ -167,7 +167,7 @@ class Task(models.Model):
         on_delete=models.SET_NULL, related_name="assignees")
     bug_tracker = models.CharField(max_length=2000, blank=True, default="")
     created_date = models.DateTimeField(auto_now_add=True)
-    updated_date = models.DateTimeField(auto_now_add=True)
+    updated_date = models.DateTimeField(auto_now=True)
     overlap = models.PositiveIntegerField(null=True)
     # Zero means that there are no limits (default)
     segment_size = models.PositiveIntegerField(default=0)