PUT endpoint does not return correct id (maybe rowid?)

Bug or feature request

• [X ] Bug
• Feature request

Description of feature (or steps to reproduce if bug)

Create a model with an id as type "string", and a defaultFN of "uuid". PUT a new instance using the REST api through explorer. The response body will show an integer id (presumably an integer that corresponds to the ROWID or something like that). Now use the GET api to list all model instances. The instance will show an id in the correct uuid format.

Link to sample repo to reproduce issue (if bug)

Expected result

I'm assuming the response body should reflect the id generated by defaultFN.

Actual result (if bug)

Its an integer.

Additional information (Node.js version, LoopBack version, etc)

Loopback 3, node 8.11.2

I'm anticipating a reply of "why are you using a string for a key?" The answer is complicated based in integration with a larger project. If the answer is "we don't support that" we'll make it work, but I wanted to check to make sure. Thanks

创建一个具有 string id 和 uuid defaultFN 的模型，然后通过 REST API Explorer 使用 PUT 提交一个新实例，以重现 LoopBack 3 案例。将 PUT 响应与通过 GET 列出实例时返回的 id 进行比较；当 PUT 响应返回生成的 UUID 而不是整数时，即表示完成。