small fix

nabirds/dataset/part/annotation.py

@@ -16,6 +16,7 @@ class LocationPart(BasePart):
 		self._id, self.x, self.y, self.is_visible = annotation
 		self._ratio = LocationPart.DEFAULT_RATIO
 
+	@property
 	def as_annotation(self):
 		return np.array([self._id, self.x, self.y, self.is_visible])