fix the breaking change in http-proxy-middleware upgrade

[marjisound]

What does this change?

The version upgrade of http-proxy-middleware in this PR #222 was causing issues in local run and couldn't proxy the requests to the correct target. This is because of a breaking change in V3 as explained in https://github.com/chimurai/http-proxy-middleware/blob/master/MIGRATION.md#removed-requrl-patching that When proxy is mounted on a path, this path should be provided in the target.

// before
app.use('/user', proxy({ target: 'http://www.example.org' }));

// after
app.use('/user', proxy({ target: 'http://www.example.org/user' }));