nextMillenium: Fixed typo. (#6224)

* updated option safeframe_ok in documentation

* fixed typo

Author: mhlm

dev-docs/bidders/nextMillennium.md

@@ -28,7 +28,7 @@ sidebarType: 1
 |----------------+----------+------------------------------------------+-----------------+-----------------|
 | `placement_id` | optional | Placement ID, provided by nextMillennium | `'12345'`       | String          |
 | `group_id`     | optional | Group ID, provided by nextMillennium     | `'12345'`       | String          |
-| `adSlots`      | optional | `adSlot` is a specific location or container on a webpage where an advertisement is displayed. | `["stickytop"]` | Array of String |
+| `adSlots`      | optional | `adSlots` is a specific location or container on a webpage where an advertisement is displayed. | `["stickytop"]` | Array of String |
 | `allowedAds`   | optional | `allowedAds` is a list of ad types or formats that are permitted to be shown in a specific ad slot. | `["skin"]`      | Array of String |
 
 Required one of the two parameters placement_id or group_id.