fix: ReactionTargetType type

[fumiama]

API好像已经变成string类型了 例：

{
  "channel_id": "xxx",
  "emoji": { "id": "277", "type": 1 },
  "guild_id": "xxx",
  "target": { "id": "xxx", "type": "ReactionTargetType_MSG" },
  "user_id": "xxx"
}