Move mvdan.cc/sh to v3

vendor/golang.org/x/xerrors/internal/internal.go

@@ -0,0 +1,8 @@
+// Copyright 2018 The Go 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 internal
+
+// EnableTrace indicates whether stack information should be recorded in errors.
+var EnableTrace = true