use dep as denpendency managment tool

vendor/github.com/ghodss/yaml/fields.go

@@ -45,7 +45,11 @@ func indirect(v reflect.Value, decodingNull bool) (json.Unmarshaler, encoding.Te
 			break
 		}
 		if v.IsNil() {
-			v.Set(reflect.New(v.Type().Elem()))
+			if v.CanSet() {
+				v.Set(reflect.New(v.Type().Elem()))
+			} else {
+				v = reflect.New(v.Type().Elem())
+			}
 		}
 		if v.Type().NumMethod() > 0 {
 			if u, ok := v.Interface().(json.Unmarshaler); ok {