correct mistake of the document

classes/class_animation.rst

@@ -24,7 +24,7 @@ An Animation resource contains data used to animate everything in the engine. An
     # 100 pixels in 1 second.
     var animation = Animation.new()
     var track_index = animation.add_track(Animation.TYPE_VALUE)
-    animation.track_set_path(track_index, "Enemy:position.x")
+    animation.track_set_path(track_index, "Enemy:position:x")
     animation.track_insert_key(track_index, 0.0, 0)
     animation.track_insert_key(track_index, 0.5, 100)