Update vendor

vendor/github.com/google/renameio/writefile.go

@@ -0,0 +1,40 @@
+// Copyright 2018 Google Inc.
+//
+// Licensed 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.
+
+// +build !windows
+
+package renameio
+
+import "os"
+
+// WriteFile mirrors ioutil.WriteFile, replacing an existing file with the same
+// name atomically.
+func WriteFile(filename string, data []byte, perm os.FileMode) error {
+	t, err := TempFile("", filename)
+	if err != nil {
+		return err
+	}
+	defer t.Cleanup()
+
+	// Set permissions before writing data, in case the data is sensitive.
+	if err := t.Chmod(perm); err != nil {
+		return err
+	}
+
+	if _, err := t.Write(data); err != nil {
+		return err
+	}
+
+	return t.CloseAtomicallyReplace()
+}