check if postgresql to fix 105 (#149)

Author: steverecio

easyaudit/migrations/0013_auto_20190723_0126.py

@@ -1,10 +1,12 @@
 # Generated by Django 2.1 on 2019-07-23 01:26
 
 from django.db import migrations, models
+from django.db import connection
 
 
 def drop_index_if_exists(apps, schema_editor):
-    schema_editor.execute('DROP INDEX IF EXISTS "easyaudit_requestevent_url_37d1b8c4"')
+    if connection.vendor == 'postgresql':
+        schema_editor.execute('DROP INDEX IF EXISTS "easyaudit_requestevent_url_37d1b8c4"')
 
 
 class Migration(migrations.Migration):