Proxy didn't work when proxy and API endpoint configs both exist

### Environment
"mocker-api": "^1.12.2"

### Issue
I have an back-end API server running locally on port 2080, and I want my front-end which running locally as well to call this local API server, because I want to do integrate test between front-end and back-end.
But I found that Proxy didn't work when proxy and API endpoint configs both exist(just returned the response.json, and API server didn't receive any request ):

(Chinese translation) 我在本地有前端和后端两个服务，后端API server运行于端口2080，如下, 如果我同时配置proxy和endpoint，只会返回`/response.json`，并没有proxy到2080的API server。这无法完成本地前后端联调测试的需求。
```java
const proxy = {
_proxy: {
proxy: {
'/api/v1/(.*)': 'http://localhost:2080/'
}
},

// API endpoint describe here
'GET /api/v1/login/:userId': (req, res) => {
return res.json(require('./response.json'));
}

};
module.exports = proxy;
```

If I remove the endpoint config, front end will call proxy which is `http://localhost:2080/`:

(Chinese translation) 如果我删除endpoint配置，只留proxy，这时`/api/v1/login/`可以转发到我的本地2080 API server中。
```java
const proxy = {
_proxy: {
proxy: {
'/api/v1/(.*)': 'http://localhost:2080/'
}
},

// API endpoint describe here (REMOVE IT !)
// 'GET /api/v1/login/:userId': (req, res) => {
// return res.json(require('./response.json'));
// }

};
module.exports = proxy;
```
Then the API server locally will receive request call for `/api/v1/login/:userId` now.

-----

Please help about what's wrong here?
Thanks

Start with the proxy and GET endpoint configuration shown in the issue, then reproduce the two cases: both entries present and the endpoint removed. Trace which route handles `/api/v1/login/:userId`; done means the behavior is explicitly resolved so the local API at `http://localhost:2080/` receives the request when both configurations are present.

Written by the indexing model from the issue text.