Change default param coordinates to 3 @turf/truncate

[DenisCarriere]

@turf/truncate coordinate param to 3

Change the default coordinates param from 2 to 3.

The GeoJSON spec suggests using 6 decimals & no more than 3 coordinates (z coordinate optional). This change prevents the "accident" (@stebogit) removal of the z coordinate.

http://geojson.org/geojson-spec.html#positions

A position is represented by an array of numbers. There must be at least two elements, and may be more. The order of elements must follow x, y, z order (easting, northing, altitude for coordinates in a projected coordinate reference system, or longitude, latitude, altitude for coordinates in a geographic coordinate reference system). Any number of additional elements are allowed -- interpretation and meaning of additional elements is beyond the scope of this specification.

Example

const pt = point([50, 40, 1100, 3000]);
//= [x, y, z, m]

Before

truncate(pt);
//= [x, y]
//= [50, 40]

Now

truncate(pt);
//= [x, y, z]
//= [50, 40, 1100]