actually use buffer geometry.

js/pixl/public/thrixl.html

				var chunk = trixl.chunks[key];
				if (chunk.dirty) {
					group.remove(chunk.geometry);
					chunk.geometry = trixl.toGeometry(chunk);
					chunk.geometry = trixl.toBufferGeometry(chunk);
					chunk.dirty = false;
					group.add(chunk.geometry);
				}