fix app.model: namespace should be unique

[sorrycc]

为啥这么改?

[MinJieLiu]

应该改为这样：

const registerModel = (app, model) => {
  // eslint-disable-next-line no-underscore-dangle
  if (!app._models.filter(m => m.namespace === model.namespace).length) {
    app.model(model);
  }
};

因为原有的：

const cached = {};
function registerModel(app, model) {
  if (!cached[model.namespace]) {
    app.model(model);
    cached[model.namespace] = 1;
  }
}

cached 变量在热更新之后会被清空掉。从而导致重复注入 model

[sorrycc]

👍