update deps

backend/vendor/github.com/xdg/stringprep/error.go

@@ -0,0 +1,14 @@
+package stringprep
+
+import "fmt"
+
+// Error describes problems encountered during stringprep, including what rune
+// was problematic.
+type Error struct {
+	Msg  string
+	Rune rune
+}
+
+func (e Error) Error() string {
+	return fmt.Sprintf("%s (rune: '\\u%04x')", e.Msg, e.Rune)
+}