Properties that are `false` only show their key name, not their value.

[BigBlueHat]

Per json-ld/json-ld.org#931

Add a test with this example JSON-LD:

{
  "x:boolF": false,
  "x:boolT": true,
  "x:numberF": 0,
  "x:numberT": 1,
  "x:listF": [],
  "x:listT": [
    1,
    2
  ]
}