update searchOptions Modifiers type

[luccacabra]

I can't find this exactly in documentation as Trello doesn't document expected API responses (🤦‍♂️ ), but when calling the search endpoint locally and via this repo, I'm getting JSON errors:

json: cannot unmarshal object into Go struct field SearchOptions.modifiers of type string

and upon further inspection of the data returned by that endpoint:

$ > curl "https://api.trello.com/1/search?query=board:test&key=XXX&token=XXX" | jq .
{
  "options": {
    "terms": [],
    "modifiers": [
      {
        "text": "board:test"
      }
    ],
    "modelTypes": [],
    "partial": false
  }
}

it appears that the modifiers data type is indeed no longer an array of strings, but an array of map[string][string]s. I've updated the SearchOptions.modifiers type to reflect that change.

[coveralls]

Coverage remained the same at 70.072% when pulling 092a6c0 on luccacabra:searchOptions-modifier into 4701389 on adlio:master.

[adlio]

Thanks for the contribution. Bug me if I don't review for merge within a few days. Hoping to review it today or tomorrow.

[adlio]

Looks good. Some additional test coverage for this would be great, but it dovetails with some testing I'm planning to do. Going to merge as-is.