Returning a JArray if multiple matching fields are found.

Changed the return type of \\\\ if multiple fields are found, so it matches the behaviour of \\.

```scala
val json = parse(
  """
    |{
    |  "aaa": [
    |     {
    |       "bbb": 100
    |     },
    |     {
    |       "bbb": 200
    |     }
    |  ]
    |}
  """.stripMargin)

json \\ "bbb"
// previous: JObject(List(("bbb", JInt(100)), ("bbb", JInt(200))))
// now: JArray(List(JInt(100), JInt(200)))

(json \ "aaa" \ "bbb") == (json \\ "bbb")  // true
```