parameters sent in the body of PUT and POST requests are not added to params

[buermann]

It would be nice to get all the request params when adding the params to the lograge message with:

     log = { params: event.payload[:params]
  end```

Which can be accomplished by accessing the `env[Grape::Env::GRAPE_REQUEST].body.read()` String::IO object in Grape::Middleware::Lograge. I will create a PR but my solution of adding it to the parameters() method feels a little clumsy.