Validations should be a list

This breaks Django2 otherwise

website/activemembers/migrations/0016_auto_20170124_1431.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.5 on 2017-01-24 13:31
+from __future__ import unicode_literals
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('activemembers', '0015_datamigration_lifelong'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='mentorship',
+            name='year',
+            field=models.IntegerField(validators=[django.core.validators.MinValueValidator(1990)]),
+        ),
+    ]

website/activemembers/migrations/0018_merge_20170125_1452.py

+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.5 on 2017-01-25 13:52
+from __future__ import unicode_literals
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('activemembers', '0016_auto_20170124_1431'),
+        ('activemembers', '0017_auto_20170121_1105'),
+    ]
+
+    operations = [
+    ]

website/activemembers/models.py

@@ -284,7 +284,7 @@ class Mentorship(models.Model):
         on_delete=models.CASCADE,
         verbose_name=_('Member'),
     )
-    year = models.IntegerField(validators=MinValueValidator(1990))
+    year = models.IntegerField(validators=[MinValueValidator(1990)])
 
     def __str__(self):
         return _("{name} mentor in {year}").format(name=self.member,