[Vendor] upgrade google/go-github to v32.1.0 (#12361)

* upgrate go-github client to v32.1.0

* migrate

vendor/github.com/google/go-github/v32/github/repos_merging.go

@@ -0,0 +1,38 @@
+// Copyright 2014 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package github
+
+import (
+	"context"
+	"fmt"
+)
+
+// RepositoryMergeRequest represents a request to merge a branch in a
+// repository.
+type RepositoryMergeRequest struct {
+	Base          *string `json:"base,omitempty"`
+	Head          *string `json:"head,omitempty"`
+	CommitMessage *string `json:"commit_message,omitempty"`
+}
+
+// Merge a branch in the specified repository.
+//
+// GitHub API docs: https://developer.github.com/v3/repos/merging/#merge-a-branch
+func (s *RepositoriesService) Merge(ctx context.Context, owner, repo string, request *RepositoryMergeRequest) (*RepositoryCommit, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/merges", owner, repo)
+	req, err := s.client.NewRequest("POST", u, request)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	commit := new(RepositoryCommit)
+	resp, err := s.client.Do(ctx, req, commit)
+	if err != nil {
+		return nil, resp, err
+	}
+
+	return commit, resp, nil
+}