boolean-valid - Allow MultiLineStrings with only a single LineString

[sharmaB01]

Fixes #2837

Why does @turf/boolean-valid require MultiLineStrings to have at least two component LineStrings? #2837

because multiline will be like

{
  "type": "MultiLineString",
  "coordinates": [
    [
      [100.0, 0.0],
      [101.0, 1.0],
      [102.0, 2.0]
    ]
  ]
}

[mfedderly]

Did some more digging and I think we need to expect 1 or more LineStrings.

If I had to guess the 2 probably came from a copy/paste error from a Position coordinates check (for a [lng, lat] pair).

Thank you!