fix a bug with pointInPolygon

Function `pnpoly` forgot to add the first point again.

See http://www.ecse.rpi.edu/Homepages/wrf/Research/Short_Notes/pnpoly.html

Otherwise, the following test will fail

```javascript
point = {"type": "Point", "coordinates": [0.5, 0.5]};

poly = {"type": "Polygon", "coordinates": [[[0, 2], [2, 2], [2,0]]]};

if (gju.pointInPolygon(point,poly)) throw new Error();
```