Fix bad variable name in TileMap documentation

doc/classes/TileMap.xml

@@ -205,7 +205,7 @@
 			<param index="2" name="atlas_coords" type="Vector2i" default="Vector2i(-1, -1)" />
 			<param index="3" name="alternative_tile" type="int" default="-1" />
 			<description>
-				Returns a [Vector2i] array with the positions of all cells containing a tile in the given layer. Tiles may be filtered according to their source ([param source_id]), their atlas coordinates ([param atlas_coords]) or alternative id ([param source_id]).
+				Returns a [Vector2i] array with the positions of all cells containing a tile in the given layer. Tiles may be filtered according to their source ([param source_id]), their atlas coordinates ([param atlas_coords]) or alternative id ([param alternative_tile]).
 				If a parameter has it's value set to the default one, this parameter is not used to filter a cell. Thus, if all parameters have their respective default value, this method returns the same result as [method get_used_cells].
 				A cell is considered empty if its source identifier equals -1, its atlas coordinates identifiers is [code]Vector2(-1, -1)[/code] and its alternative identifier is -1.
 			</description>