fix camera rotation direction.

js/pixl/public/trixl.html

			var front = trixl.camera.front();
			var strafe = trixl.camera.strafe(front);
			trixl.camera.rotateAround(dx, trixl.camera.up);
			trixl.camera.rotateAround(dy, strafe);
			trixl.camera.rotateAround(-dx, trixl.camera.up);
			trixl.camera.rotateAround(-dy, strafe);
		}
		trixl.camera.rotateAround = function(angle, axis) {
			var front = trixl.camera.front();