Update default validator's docs link (#2738)

The default validator has upgraded from v8 to v10, but its docs link didn't.

binding/default_validator.go

@@ -71,7 +71,7 @@ func (v *defaultValidator) validateStruct(obj interface{}) error {
 // Engine returns the underlying validator engine which powers the default
 // Validator instance. This is useful if you want to register custom validations
 // or struct level validations. See validator GoDoc for more info -
-// https://godoc.org/gopkg.in/go-playground/validator.v8
+// https://pkg.go.dev/github.com/go-playground/validator/v10
 func (v *defaultValidator) Engine() interface{} {
 	v.lazyinit()
 	return v.validate