Update tengo vendor and load the stdlib. Fixes #789 (#792)

vendor/github.com/d5/tengo/stdlib/errors.go

@@ -0,0 +1,11 @@
+package stdlib
+
+import "github.com/d5/tengo/objects"
+
+func wrapError(err error) objects.Object {
+	if err == nil {
+		return objects.TrueValue
+	}
+
+	return &objects.Error{Value: &objects.String{Value: err.Error()}}
+}