Disable merge button for PRs (#2041)

diff --git a/.asf.yaml b/.asf.yaml
index db175df..2c7272d 100644
--- a/.asf.yaml
+++ b/.asf.yaml
@@ -1,5 +1,31 @@
-notifications:

-    commits:      commits@dubbo.apache.org

-    issues:       notifications@dubbo.apache.org

-    pullrequests: notifications@dubbo.apache.org

-    jira_options: link label link label

+#
+# 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.
+#
+
+github:
+    enabled_merge_buttons:
+        # enable squash button:
+        squash:  true
+        # enable merge button:
+        merge:   false
+        # disable rebase button:
+        rebase:  false
+
+notifications:
+    commits:      commits@dubbo.apache.org
+    issues:       notifications@dubbo.apache.org
+    pullrequests: notifications@dubbo.apache.org
+    jira_options: link label link label