Merge heads (#6729)

* Merge heads

* Add ASF header

superset/migrations/versions/18dc26817ad2_.py

+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+"""empty message
+
+Revision ID: 18dc26817ad2
+Revises: ('8b70aa3d0f87', 'a33a03f16c4a')
+Create Date: 2019-01-18 14:56:26.307684
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '18dc26817ad2'
+down_revision = ('8b70aa3d0f87', 'a33a03f16c4a')
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    pass
+
+
+def downgrade():
+    pass