Fix relative import in plugin (#426)

plugins/databricks/databricks_operator.py

@@ -26,7 +26,7 @@ import six
 import time
 
 from airflow.exceptions import AirflowException
-from .databricks_hook import DatabricksHook
+from databricks.databricks_hook import DatabricksHook
 from airflow.models import BaseOperator
 from airflow.utils.decorators import apply_defaults