replacing call to Index.get_sql_create_template_values with Index.create_sql for Django 2.2 compatibilty

Author: sp-mmartin

django_celery_beat/models.py

@@ -49,11 +49,7 @@ def _is_mysql_backend(self, connection):
 
     def _create_sql(self, model, schema_editor, using=''):
         sql_create_index = 'CREATE INDEX %(name)s ON %(table)s (%(columns)s(%(size)d))%(extra)s'
-        sql_parameters = self.create_sql(
-            model,
-            schema_editor,
-            using
-        )
+        sql_parameters = super(CeleryMySQLIndex, self).create_sql(model, schema_editor, using=using)
         sql_parameters['size'] = getattr(
             settings,
             'DJANGO_CELERY_BEAT_NAME_MAX_LENGTH',