remove a call to StructField.IsExported as it is not in go1.13

Author: huandu

struct.go

@@ -437,7 +437,7 @@ func (s *Struct) Values(st interface{}) []interface{} {
 	return s.ValuesForTag("", st)
 }
 
-// Values returns a shadow copy of all fields tagged with tag in st.
+// ValuesForTag returns a shadow copy of all fields tagged with tag in st.
 func (s *Struct) ValuesForTag(tag string, value interface{}) (values []interface{}) {
 	sf := s.structFieldsParser()
 	v := reflect.ValueOf(value)

structfields.go

@@ -52,7 +52,7 @@ func (sf *structFields) parse(t reflect.Type, mapper FieldMapperFunc, prefix str
 		field := t.Field(i)
 
 		// Skip unexported fields that are not embedded structs.
-		if !field.IsExported() && !field.Anonymous {
+		if field.PkgPath != "" && !field.Anonymous {
 			continue
 		}