Add Optional Params to Concert Adapter

[jeninedrew]

Type of change

• Feature
• Does this change affect user-facing APIs or examples documented on http://prebid.org?

Description of change

Add optional params to Concert adapter.

• test parameters for validating bids

  var adUnits = [
    {
      code: 'desktop_leaderboard_variable',
      mediaTypes: {
        banner: {
          sizes: [[1030, 590]]
        }
      }
      bids: [
        {
          bidder: "concert",
          params: {
            partnerId: 'test_partner',
            site: 'site_name',
            placementId: 1234567,
            slot: 'slot_name',
            sizes: [[1030, 590]]
          }
        }
      ]
    }
  ];
}

• contact email of the adapter’s maintainer: support@concert.io

For any changes that affect user-facing APIs or example code documented on http://prebid.org, please provide:

• A link to a PR on the docs repo: Update Concert Adapter prebid.github.io#2542

[lgtm-com]

This pull request introduces 4 alerts when merging 6ba431c into 6963bb3 - view on LGTM.com

new alerts:

• 4 for Property access on null or undefined

[ncolletti]

LGTM