Add migration for slack_channel field update.

hypha/apply/funds/migrations/0075_auto_20200629_1707.py

+# Generated by Django 2.2.13 on 2020-06-29 17:07
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('funds', '0074_add_word_limit_to_text_blocks'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='applicationbase',
+            name='slack_channel',
+            field=models.CharField(blank=True, help_text='The slack #channel for notifications. If left empty, notifications will go to the default channel.', max_length=128),
+        ),
+    ]