Support lists in query variables (Dgraph's GraphQL Variable)

MichelDiz commented :

This works

query query($uids: string = "[0x1, 0x2, 0x3]") {
  query(func: uid($uids)) {
    uid
  }
}

so, what needs to change, and not confuse future users, is the uid part. I gonna add references about this there.