Adjust `meta` response section to be a document rather than an array

[erikhatcher]

Currently it looks like this:

 "meta": [
   {
     "count": {
       "total": 2
     }
   }
 ]

[erikhatcher]

Add this to the pipeline:

{
   "$set": {
     "meta": {
       "$arrayElemAt": ["$meta", 0]
     }
   }
 }