small fixes for django 2.0

src/membership/migrations/0008_auto_20190106_1954.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.1.5 on 2019-01-06 18:54
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('membership', '0007_auto_20171115_0653'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='membership',
+            name='last_name',
+            field=models.CharField(blank=True, max_length=150, verbose_name='last name'),
+        ),
+    ]