[3.0] Use the package 'method-override'

Replace `loobpack.methodOverride()` with using `method-override`
directly in order to prevent a warning from connect.

```
connect deprecated methodOverride: use method-override module directly app.js:42:18
```

/to @ritch please review

I am not sure if this should be fixed here, or rather in loopback 1.x. `loopback 2.x` already has a code to expose 'method-override' as `loopback.methodOverride`, perhaps we can back-port it to 1.x

Thoughts?

/cc @raymondfeng