Vendor in containers/buildah 1.16.1

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

vendor/github.com/containers/buildah/copier/unwrap_113.go

@@ -0,0 +1,18 @@
+// +build go113
+
+package copier
+
+import (
+	stderror "errors"
+
+	"github.com/pkg/errors"
+)
+
+func unwrapError(err error) error {
+	e := errors.Cause(err)
+	for e != nil {
+		err = e
+		e = errors.Unwrap(err)
+	}
+	return err
+}